Development of Self-Stabilizing Manipulator Inspired by the Musculoskeletal System Using the Lyapunov Method

Chang, Handdeut,Kim, Sangjoon Jonathan,Kim, Jung IEEE 2017 IEEE TRANSACTIONS ON ROBOTICS Vol.33 No.6

<P>The stabilization of man-made dynamic systems has been achieved by sensor-based state feedback control with high computational bandwidth, fast signal transmission speed, and stiff joints. In contrast, many biological systems can achieve similar or superior stable behavior with low computational bandwidth, slow signal transmission speed via the nervous system, and flexible joints. The concept of self-stabilization has recently been proposed and widely investigated to explain this phenomenon. Self-stabilization is defined as the ability to restore its original state after a disturbance without any feedback control. In this paper, the stabilizing function of a musculoskeletal system for arbitrary motion in the vertical plane is analytically investigated using Lyapunov stability criteria. Based on this investigation, the method of designing a new actuator that can assign a self-stabilizing function to a robotic arm is introduced and a self-stabilizing manipulator is physically realized. As a result, a theoretically predicted self-stabilizing function is experimentally verified and explains why a biological musculoskeletal system can be stabilized with feedforward control.</P>

Development of Active Stiffness Mechanism for Self-stabilizing Manipulator

Handdeut Chang,Sangjoon J. Kim,Jung Kim 제어로봇시스템학회 2016 제어로봇시스템학회 국제학술대회 논문집 Vol.2016 No.10

The stabilization of most artificial systems has been achieved by sensor based state feedback control with high signal transmission speed and high computational power, and stiff structures. In contrast, many biological systems can achieve similar or superior stable behavior with low signal transmission speed and low computational power via nervous system, and flexible structures. In order to explain this phenomenon, our research group focused the concept of self-stabilization of musculoskeletal system. Self-stabilization is defined as the ability to restore its original state after a disturbance with feedforward control. In our previous research, we analytically investigated the self-stabilizing condition of biological musculoskeletal system using the Lyapunov stability criteria and come to a conclusion that stiffness and viscosity of the joint play significant role in self-stabilization. Particularly, there exist two types of stiffness in biological muscle; one is spring-like passive stiffness and the other is active stiffness that is proportional to muscle activation. We believe that active stiffness plays a significant role in self-stabilization for dynamic movement. In this paper, we develop an active stiffness mechanism that can assign self-stabilizing function to a robotic arm. As a result, theoretically predicted self-stabilizing function is experimentally verified and explains why biological musculoskeletal system can be stabilized with feedforward control.

Development of a Variable Stiffness Modulating Mechanism Based on Phase-Change Material and a Temperature Control System

Quang Ngoc Le,Hyunho Kim,Sanghun Jeong,Handdeut Chang,Hardik J. Pandya,Yeongjin Kim 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.23 No.5

One of the challenges of using an endoscopic robot for natural orifice transluminal endoscopic surgery (NOTES) is the ability to adjust its joint stiff ness. The endoscopic robot joint needs low stiff ness to move through paths in the human body without damaging tissues and high stiff ness to keep its shape. This paper presents a variable stiff ness manipulator for the endoscopic robot in NOTES. The manipulator has a backbone tube that uses a thermoplastic material, polyethylene terephthalate glycol (PETG), with a temperature effect to change the stiff ness. The backbone of the robot is designed with a heating coil, cooling tube, and thermal sensor to adjust the temperature. Analysis and experiments were conducted to evaluate and find the backbone structure with a large range of stiff ness modulations, a short heating time, and a short cooling time. This paper also presents a temperature control system that controls the temperature to maintain the stiff ness of the robot in real-time. The stiff ness characterization, heating time, and cooling time of the robot and the response of the temperature controller, are tested experimentally. The results confirm that the endoscopic robot can be changed and maintained at some stiff ness values.

Characterization of Spastic Ankle Flexors Based on Viscoelastic Modeling for Accurate Diagnosis

신원석,Handdeut Chang,Sangjoon J. Kim,김정 제어·로봇·시스템학회 2020 International Journal of Control, Automation, and Vol.18 No.1

Characterization of the musculoskeletal system is essential for diagnosis providing the implications for therapy corresponding to causes of the diseases. This paper presents a characterization of an ankle neuromuscular system of patients with spasticity, to provide quantitative pathological level of the ankle spasticity with biomechanical and neurological disorders. Measurements from manual spasticity evaluation combined with a suggested neuromuscular model and parameter optimization process enabled a reliable characterization of the spastic ankle flexors. The model included two non-neural parameters representing the viscoelasticity of the muscle and four neural parameters showing the dynamics of muscle activation and corresponding force only using the measured joint angle and resistance torque. Torque contributions from non-neural parameters especially elastic properties of muscle was greater than 50% of the overall torque, common in both patients with spasticity and healthy controls. Among subgroups of the patients, subjects with short post diseases period less than 5 years, had higher torque contribution level from neural components more than 50% of the overall torque compared to the patients with longer post diseases period more than 10 years who had overall torque less than 30% of the total estimated torque. We concluded that proposed model based ankle flexor characterization served as a tools for diagnosing the patients with spasticity corresponding to their causes of diseases with both quantified neural and non-neural parameters.

Development of Particle Flow-Based Inflatable Robot Body for Shape Rigidity Modulation

Hyunho Kim,Sangjoon Jonathan Kim,Junghoon Park,Handdeut Chang,Namkeun Kim,Yeongjin Kim 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.10

Disaster robots are needed to perform various tasks through narrow gaps between building debris to be used for rescue. A soft material-based disaster robot can have easy access to the rescue site through the narrow gaps. To ensure the robust control and better performance of the soft robot operation, a joint stiff ness modulation mechanism is required. In this paper, we have proposed a noble stiff ness modulation mechanism that includes shape change and self-assembly by using a particle flow-based inflatable robot body. We analyzed the particle filling completion time by injecting air and particles at a constant pressure into the soft chamber depending on several parameters (the size of the particle, the size of the reservoir, the volume ratio between the chamber volume and the total volume of the particle, and the injected air pressure). Of these, the most dominant factors influencing the completion time were particle size and pressure. It was observed that the smaller the size of the particle, the shorter time. The completion time tended to decrease as the air pressure increased.

Development of a compact optical torque sensor with decoupling axial-interference effects for pHRI

Lee, Hyein,Kim, Sangjoon J.,Chang, Handdeut,Kim, Jung Elsevier 2018 Mechatronics Vol.52 No.-

<P>This paper presents the design of an optical torque sensor that can structurally decouple the effect of axial-interference for use in various robotics applications. Torque sensors are widely used in the joints of intelligent service or wearable robots to realize safe human-robot interaction. Whole robot body sensing using torque sensors is essential for safe interaction. However, most torque sensors are bulky, heavy and expensive. Therefore, many optical-based torque sensors have been proposed to deal with such problems, but the issue of axial-interference still remains. We resolved the axial-interference problem via the geometrical structure of the sensor body and differential signaling using two reflective optical sensors. The moment interference error was successfully decreased from 4.49% (with one optical sensor) to 0.11% (with two optical sensors) using the proposed sensor structure while maintaining a compact size, lightweight, and low cost. Static tests and dynamic tests were carried out and analyzed for accuracy error, hysteresis, and repeatability. We then compared the performance of an impedance controller that is widely used in service and wearable robots using the proposed sensor and a commercial torque sensor with respect to various control loop rates. The control performance of the proposed sensor was comparable to that of commercial sensors.</P>