Doyoung Jeon

Design and control of an exoskeleton for the elderly and patients

Recently, the exoskeletal power assistive equipment, which is a kind of wearable robot, has been widely developed to help human body motion. The exoskeleton for elderly people and patients, however, has some limitations due to the weight and volume of the equipment. In this paper, a tendon-driven exoskeletal power assistive device, exoskeleton for patients and the old by the Sogang University (EXPOS), is proposed as a feasible solution. In case of EXPOS, the caster walker carries heavy items such as motors, drivers, controllers, and batteries so that the weight and volume of the wearable exoskeleton are minimized. The tendon-connecting motors and pulleys of hip and knee generate the assistive power according to the requirement of the users. In this paper, the design concepts of the EXPOS, sensing techniques, and control methods are discussed

Design Analysis and Experimental Evaluation of an MR Fluid Clutch

An MRC (Magneto-Rheological Clutch), a device to transmit torque by shear stress of MR fluids, has the property that its power transmissibility changes quickly in response to control signal. In this study, we consider methods to predict performance of an MRC. First, we anticipate the performance of an MRC with a simplified mathematical model and second, we predict the performance in consideration of the applied magnetic field and viscosity distribution of fluids caused by the field. Between the two methods, compared with experimental results, it is shown that the numerical method is closer to reality than the simplified one.

Impedance Compensation of SUBAR for Back-Drivable Force-Mode Actuation

The Sogang University biomedical assistive robot (SUBAR), which is an advanced version of the exoskeleton for patients and the old by Songang (EXPOS) is a wearable robot developed to assist physically impaired people. It provides a person with assistive forces controlled by human intentions. If a standard geared DC motor is applied, however, the control efforts will be used mainly to overcome the resistive forces caused by the friction, the damping, and the inertia in actuators. In this paper, such undesired properties are rejected by applying a flexible transmission. With the proposed method, it is intended that an actuator exhibits zero impedance without friction while generating the desired torques precisely. Since the actuation system of SUBAR has a large model variation due to human-robot interaction, a control algorithm for the flexible transmission is designed based on a robust control method. In this paper, the mechanical design of SUBAR, including the flexible transmission and its associated control algorithm, are presented. They are also verified by experiments.

A rotational micro biopsy device for the capsule endoscope

Recently the technology of capsule endoscopy has developed dramatically and many researchers are making efforts to combine surgical function into the capsule type endoscope. In this paper, the micro biopsy module which is a part of the capsule endoscope is proposed. The proposed module is less than 2 mm in thickness and has a diameter of 10 mm. It consists of a trigger with paraffin block, rotational tissue-cutting razor with a torsion spring and controller. This module makes it possible for the capsule endoscope to obtain a sample tissue inside the small intestine which can not be reached by a conventional biopsy device. Through dedicated experiments, tissue samples were successfully extracted using the proposed biopsy module and the cells in samples were extracted and tested by a microscope.

Fuzzy Control of a New Tendon-Driven Exoskeletal Power Assistive Device

This paper proposes a tendon-driven exoskeletal power assistive device to reduce some problems of the existing exoskeletal power assistive equipment. In addition, this paper suggests a caster walker carrying heavy peripheral devices and maintaining stable balance of the user at the same time. A muscle fiber expansion signal is used to control this device in order to compensate for the delay time of motors and perform an easy assistance by sensing the users action in advance. The muscle fiber expansion signal has the characteristics that the signal is ahead of action and in proportion to joint torque. A fuzzy control method is applied to control the proposed exoskeletal assistive device. This paper also describes a number of action tests such as sitting, standing, and walking. The experimental results were quantitatively evaluated by comparing the EMG signal before and after wearing of the proposed exoskeletal assistive device.

Semiactive Vibration Control of a Smart Seat with an MR Fluid Damper Considering its Time Delay

The Lyapunov type robust control is applied to the semiactive vibration control of a controllable seat system to accommodate the modelling uncertainty of system and time delay of the damper. The seat system has a flexible mechanism of a spring and MR fluid damper between a seat cushion and base. Simulation results show that the robust control considering the time delay of the damper suppresses the seat vibration effectively.

Vibration suppression in an MR fluid damper suspension system

An MR(Magneto-Rheological) fluid damper is designed and applied to a semi-active suspension system of a quarter car model. The damping constant of the MR damper changes according to the input current and the time delay of the damper is included in the system dynamics. The passive method, LQ control and frequency shaped LQ control are compared in experiments. The advantage of the proposed frequency shaped LQ control is that the ride comfort improves in the frequency range of 4 and 8 Hz where a human is most sensitive and the driving safety improves around the resonance frequency of unsprung mass, 11 Hz. The experiments using a quarter car model show the effectiveness of the algorithm.

A Robotic Biopsy Device for Capsule Endoscopy

This paper introduces a robotic biopsy device for capsule endoscopes. The proposed device consists of three modules for the complete process of biopsy, which includes monitoring the intestinal wall by a tissue monitoring module (TMM), aligning onto a polyp by an anchor module (AM), and sampling of the polyp tissue by a biopsy module (BM). The TMM utilizes a trigonal mirror as well as an on-board camera; since the TMM continuously takes images through lateral apertures, an operator such as a medical doctor is able to anchor the capsule endoscope onto the polyp and biopsy it with the visual feedback in real-time. When the operator finds a polyp using the TMM and the frontal camera of a capsule endoscope, then the AM is used to approach the polyp for biopsy. When the AM is in use, outriggers are extruded by shape-memory-alloy (SMA) springs, which results in the swelling of capsule endoscope body. In addition, an alignment module, which is a part of the AM, rotates the body of the capsule endoscope such that the biopsy razor can be aligned onto the polyp. Then, the BM excises a part of the polyp and seals the aperture, and the capsule endoscope continues exploring the intestine. The concept and working principles of the proposed device are introduced in this paper and are verified by a prototype that successfully integrates the three modules.

Barbed micro-spikes for micro-scale biopsy

Single-crystal silicon planar micro-spikes with protruding barbs are developed for micro-scale biopsy and the feasibility of using the micro-spike as a micro-scale biopsy tool is evaluated for the first time. The fabrication process utilizes a deep silicon etch to define the micro-spike outline, resulting in protruding barbs of various shapes. Shanks of the fabricated micro-spikes are 3 mm long, 100 ?m thick and 250 ?m wide. Barbs protruding from micro-spike shanks facilitate the biopsy procedure by tearing off and retaining samples from target tissues. Micro-spikes with barbs successfully extracted tissue samples from the small intestines of the anesthetized pig, whereas micro-spikes without barbs failed to obtain a biopsy sample. Parylene coating can be applied to improve the biocompatibility of the micro-spike without deteriorating the biopsy function of the micro-spike. In addition, to show that the biopsy with the micro-spike can be applied to tissue analysis, samples obtained by micro-spikes were examined using immunofluorescent staining. Nuclei and F-actin of cells which are extracted by the micro-spike from a transwell were clearly visualized by immunofluorescent staining.

A generalized control framework of assistive controllers and its application to lower-limb-exoskeletons

Various control methods have been studied for the natural assistance of human motions by exoskeletal robots, i.e., wearable robots for assisting the human motions. For example, impedance control and compliance control are widely used for controlling interaction forces between a human and a robot. When an accurate measurement of the human muscular force is available (e.g., electromyography), a direct use of the estimated human joint torque is possible in the control of an assistive robot. The human motions in a daily living, however, are so complex that they are constituted by multiple phases, such as walking, sitting, and standing, where the walking can be further categorized into multiple sub-phases. Therefore, a single control method cannot be the best option for all the motion phases; a switch in the control algorithms may be necessary for assisting human movements in multiple motion phases. In this paper, a generalized control framework is proposed to incorporate the various assistive control methods in one general controller structure, which consists of Feedforward Disturbance Compensation Control, Reference Tracking Feedback Control, Reference Tracking Feedforward Control, Model-based Torque Control. The proposed control framework is designed taking into consideration of the linearity of each control algorithm, and thus it enables the continuous and smooth switching of assistive control algorithms, and makes it possible to analyze the stability of the overall control loop. The proposed method is implemented into a lower-limb exoskeleton robot and is verified by experimental results. A generalized control framework is proposed to incorporate the various assistive control methods in one general controller structure.The proposed control framework enables the continuous and smooth switching of assistive control algorithms.The proposed control framework makes it possible to analyze the stability of the overall control loop.The proposed method is implemented into a lower-limb exoskeleton robot and is verified by experimental results.