Frequency-Shaped Impedance Control for Safe Human–Robot Interaction in Reference Tracking Application

Sehoon Oh,Hanseung Woo,Kyoungchul Kong IEEE 2014 IEEE/ASME transactions on mechatronics Vol.19 No.6

<P>In the control of industrial robots, both safety and reference tracking performance are required. For safe human-robot interaction, robots should exhibit low mechanical (or controlled) impedance so that they react to the interaction forces in a compliant manner. On the other hand, the reference tracking requires for the robots to reject exogenous disturbances, which results in an increased impedance. In order to achieve these two conflicting objectives, a frequency-shaped impedance control (FSIC) method is proposed in this paper. The proposed method utilizes the two different functionalities of the disturbance observer (DOB): a disturbance estimation function as an observer and a disturbance rejection function as a feedback controller. Namely, the DOB is utilized as an observer at the frequencies where the robots interact with humans, while it is used as a feedback controller (i.e., disturbance rejection controller) at the frequencies where the reference tracking is required. The proposed approach is realized by shaping a filter of the DOB in the frequency domain so that the impedance is manipulated to achieve both the compliant interaction and reference tracking. The compromised reference tracking performance in the frequency range, where the impedance is set low, can also be supplemented by feedforward control. A typical feedback controller and a feedforward controller are designed in addition to the DOB-controlled system as the whole control system to enhance reference tracking performance and the betterment of stability robustness. The proposed method is verified by experimental results in this paper.</P>

Dynamic Analysis of Series Elastic Actuator in Terms of Controller Design

Sehoon Oh,Kyoungchul Kong 제어로봇시스템학회 2016 제어로봇시스템학회 국제학술대회 논문집 Vol.2016 No.10

In order to provide highly compliant and powerful force, a series elastic actuator (SEA) has been developed and are now widely utilized. In spite of this characteristics as an ideal force source for safe human-robot interactions, SEA is considered difficult to design and control as its mechanical structure is complicated, namely it consists of a motor, a reduction gear, an elastic element and load, which causes various challenges, such as the unknown dynamics of a load, the nonlinearity of gears, the oscillation mode induced by the elastic element, and so on. It is required to investigate how the dynamic characteristics are influenced by these issues, and this paper tackles this problem by deriving and analyzing the dynamics of SEA. The dynamics of SEA with mechanical parameter variations is evaluated using the criteria utilized for controller design.

Frequency-Shaped Impedance Control for Safe Human-Robot Interaction in Reference Tracking Application

Sehoon Oh,Hanseung Woo,Kyoungchul Kong 제어로봇시스템학회 2014 제어로봇시스템학회 국제학술대회 논문집 Vol.2014 No.10

In the control of industrial robots, both safety and reference tracking performance are required. For safe human-robot interaction, robots should exhibit low mechanical (or controlled) impedance so that they react to the interaction forces in a compliant manner. On the other hand, the reference tracking requires for the robots to reject exogenous disturbances, which results in an increased impedance. In order to achieve these two conflicting objectives, a frequencyshaped impedance control (FSIC) method is proposed in this paper. The proposed method utilizes the two different functionalities of the disturbance observer (DOB): a disturbance estimation function as an observer and a disturbance rejection function as a feedback controller. Namely, the DOB is utilized as an observer at the frequencies where the robots interact with humans, while it is used as a feedback controller (i.e., disturbance rejection controller) at the frequencies where the reference tracking is required. The proposed approach is realized by shaping a filter of the DOB in the frequency domain so that the impedance is manipulated to achieve both the compliant interaction and reference tracking. The compromised reference tracking performance in the frequency range, where the impedance is set low, can also be supplemented by feedforward control. A typical feedback controller and a feedforward controller are designed in addition to the DOB-controlled system as the whole control system to enhance reference tracking performance and the betterment of stability robustness. The proposed method is verified by experimental results in this paper.

Development of Golden Section Search Driven Particle Swarm Optimization and its Application

Sehoon Oh,Yoichi Hori 제어로봇시스템학회 2006 제어로봇시스템학회 국제학술대회 논문집 Vol.2006 No.10

High-Precision Robust Force Control of a Series Elastic Actuator

Oh, Sehoon,Kong, Kyoungchul IEEE 2017 IEEE/ASME transactions on mechatronics Vol.22 No.1

<P>A series elastic actuator (SEA) is a promising actuation method in force control applications that intelligently interacts with environments. The SEA is characterized by a spring placed between a load and an actuator, which is an electric motor in most cases. Since the spring plays the role of a transducer between position (i.e., the spring deflection) and force, it is able to control the output force (torque) precisely by utilizing typical position control methods. However, the force control performance of the SEA is considered to have limitations due to its elasticity, and thus, to be inferior to rigid actuators in terms of bandwidth. This paper proposes that the force control performance of the SEA can be improved by exploiting the dynamic model of the SEA. To this end, the SEA is modeled and analyzed utilizing the two-mass dynamic model, which is a well-known and widely accepted model of the flexible system. The disturbance observer and feedforward controller are introduced as the model-based control algorithms for the SEA to achieve the high-precision force control. In addition to high-bandwidth force control, the proposed controller can address the robust stability and performance against model parameter variance and exogenous disturbances. For the analytic and quantitative assessment of the proposed force control system, the dynamic characteristics of an SEA under various control algorithms are analyzed, and the experimental results are provided for an actual SEA system in this paper.</P>

Fractional Order Impedance Control by Particle Swarm Optimization

Sehoon Oh,Yoichi Hori 제어로봇시스템학회 2008 제어로봇시스템학회 국제학술대회 논문집 Vol.2008 No.10

This paper suggests a methodology to realize fractional order impedance using feedback control of a motor, which can be called fractional impedance control. First, a novel discretization method of a fractional order integrator is proposed based on the coefficient fitting by particle swarm optimization. Based on this fractional order integrator, fractional order impedance control is realized using feedback control design. The characteristics of fractional impedance are analyzed by simulations, and the algorithm is implemented in a motor and the characteristics are made clear by experiments

A mechanism for orbital angular momentum and giant spin-splitting in solids and nanostructures

Sehoon Oh,Hyoung Joon Choi 한국자기학회 2015 한국자기학회 학술연구발표회 논문개요집 Vol.2015 No.11

Two-Degree-of-Freedom Control of a Two-Link Manipulator in the Rotating Coordinate System

Sehoon Oh,Kyoungchul Kong Institute of Electrical and Electronics Engineers 2015 IEEE transactions on industrial electronics Vol. No.

<P>As applications and tasks of robotic manipulators become more diverse and complicated, the desired motions of the robots also become more sophisticated and complicated. In spite of this diversity of tasks, the coordinate system to describe the tasks has not been changed much; the conventional Cartesian coordinate system is still the most widely used coordinate system. It is found in this paper that the rotating coordinate system significantly simplifies the kinematics of a two-link robotic manipulator with the biarticular actuation coordination, which is inspired from human muscles that can generate torques at adjoining two joints simultaneously. Taking the advantage of this simple kinematic relationship by the rotating coordinate system and the biarticular actuator coordination, the dynamics of the two-link manipulator is analyzed, and a disturbance observer (DOB) is designed based on the derived dynamics to nominalize the actual dynamics and to reject undesired disturbances. The proposed DOB-based control algorithm can achieve better control performance in the rotating coordinate system, and comparative experiments verify the effectiveness of the proposed coordinate system and control methods.</P>

Design and Analysis of Force-Sensor-Less Power-Assist Control

Sehoon Oh,Kyoungchul Kong,Hori, Yoichi IEEE 2014 IEEE transactions on industrial electronics Vol.61 No.2

<P>Due to the recent trend of the application of robots and other mechatronic devices to human life support, the force control draws more attention than ever. However, to use force sensors in all the required cases makes the system not only expensive but also bulky. Force-sensor-less power-assist control (FSPAC) which uses only encoders to obtain the external force information and provides force control performance can address this problem. Due to its simplicity and wide application, FSPAC is an essential technology to control a motor in a human-friendly way, but the design of FSPAC is different from the conventional feedback controllers so a new design methodology needs to be established. In order to attack this problem, this paper generalizes and analyzes the structure and characteristics of FSPAC. The generalized structure reveals how FSPAC can achieve the assistance, and the transfer function analysis based on the structure addresses the robustness and assistance performance evaluation problems. The robustness of FSPAC is analyzed in terms of the gain margin and robust stability, and the limitation of the power assistance to guarantee the robust stability is derived. Then, the evaluation way of feedback control design in FSPAC is provided. All the discussion in this paper provides the readers with understanding and appropriate design methodology of FSPAC.</P>

로봇기술을 이용한 Steer-by-Wire 시스템 개발

오세훈(Sehoon Oh),천다솔(Dasol Cheon) 한국자동차공학회 2021 오토저널 Vol.43 No.2