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.

Super Twisting Sliding Mode Control-Based Impedance Control for Teleoperated Virtual Robot Arm End-Effector Force Tracking

Hamza Khan,Saad Jamshed Abbasi,Muhammad Salman,Min Cheol Lee 제어로봇시스템학회 2022 제어로봇시스템학회 국제학술대회 논문집 Vol.2022 No.11

In this research, a virtual simulator (slave system) of an eight-degrees-of-freedom robot (two-DOF crane, one-DOF prismatic (telescopic mast), and five-DOF robot manipulator) is developed and teleoperated by an external hardware haptic device (master system) for nuclear power plants (NPP) reactor vessel internals (RVI) dismantling operations. For operations such as cutting, the robot end-effector with a laser cutter should maintain a constant distance from the physical wall of RVI. So, a virtual wall near the physical wall is assumed. The end-effector should remain on the virtual wall for optimal cutting which is achieved through force tracking impedance control. In this paper, initially sliding mode control (SMC) was implemented but resulted in chattering in force tracking response. Therefore, super twisting sliding mode control (STSMC)-based force tracking impedance control is designed and implemented for enhanced end-effector force tracking. The control input of the STSMC is composed of a continuous and discrete component. Continuous control input regulates control performance against uncertainties, whereas discrete provides a switching algorithm. STSMC then eliminates the chattering effect and reduces the force tracking error. The performance of SMC-based and STSMC-based impedance control is compared, and the comparison shows that the STSMC-based impedance control provides enhanced performance.

Admittance Force Tracking Control Schemes for Robot Manipulators under Uncertain Environment and Dynamics

Seul Jung,Do-Jin Jeong 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.11

Force control for robot manipulators is increasingly demanded for stable and desired interaction between robots and environments. In this paper, several modifications of an admittance force control scheme are presentedand derived from force tracking impedance functions to give a force tracking capability to position-controlled robot manipulators. Admittance force control known as the position-based force control has a structural advantage ofeasy implementation for the force control capability to the existing position-controlled robot systems by closing an outer force control loop. The admittance filter as an inverse of impedance function is implemented to filterforce errors to modify the reference position such that the eventual force tracking impedance control is realized indirectly. Admittance filters are formulated from impedance functions that guarantee the desired force/positiontracking performances with the help of the time-delayed controller. Desired contact force/position tracking control is achieved under uncertain environment and dynamics. Extensive simulation studies of force/position tracking controlperformances of the proposed control schemes for a robot manipulator are conducted to confirm the proposition.

Learning-based Adaptive Optimal Impedance Control to Enhance Physical Human-robot Interaction Performance

Yida Guo,Yang Tian,Haoping Wang 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.9

This paper presents a framework of adaptive optimal impedance control to enhance physical humanrobot interaction (pHRI) performance. The overall structure of the proposed control scheme consists of an outer control loop and an inner control loop. In the outer control loop, a cost function that considers human motion and interaction force is minimized to optimize the overall human-robot interaction performance. An adaptive impedance controller is designed based on a Q-learning algorithm to realize impedance adaptation and guarantee the impedance parameters converge to the optimal value with completely unknown dynamics of the human limb. Then, a torque controller is developed in the inner control loop to enable the robot respond follow the obtained impedance model. In this controller, a novel barrier Lyapunov function (BLF) is employed to guarantee the error constraint and radial basis function neural networks (RBFNNs) are utilized to approximate the unknown robot dynamics. Stability and uniform boundedness of the closed-loop system are validated. Numerical simulation studies are performed to verify the effectiveness of the proposed controller.

Variable Impedance Control and Fuzzy Inference Based Identification of User Intension for Direct Teaching of a Mobile Robot

고종현(Jong Hyeon Ko),배장호(Jang Ho Bae),홍대희(Daehie Hong) Korean Society for Precision Engineering 2016 한국정밀공학회지 Vol.33 No.8

Controlling a mobile robot using conventional control devices requires skill and experience, and is not intuitive, especially in complex environments. For human-mobile robot cooperation, the direct-teaching method with impedance control has been used most frequently in complex environments. This thesis proposes a new direct-teaching method for a mobile robot utilizing variable impedance control. This includes analysis of user intention, which is changed by force and moment. A fuzzy inference technique is proposed in this thesis for identification of user intension. The direct teaching of a mobile robot based on variable impedance control through fuzzy inference is experimentally verified by comparing its efficiency to that of the conventional impedance control-based direct teaching of a mobile robot. Experimental data, such as the total time consumed, path error time, and the total energy used by the user, were recorded. The results showed that the efficiency of variable impedance control was increased.

Adaptive Quasi-PRD Control Method of Grid - Connected PV Inverter Under Weak Grid

Xiaojiao Cao,Guihua Liu,Weinan Xu,Wei Wang 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

The high grid impedance in weak grid will lead to small bandwidth of control system and poor control performance of PV inverter. To solve this problem, this paper presents a quasi-PRD control method which can increase the bandwidth and dynamic response speed of control system. At first, the quasi-PRD controller was applied to replace the traditional PI controller. Then, the two harmonic injection method was used to detect grid impedance online which would be used to adjust the controller parameters adaptively. At last, some simulation and experiments were done to verify the validity of the novel control method.

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

Intelligent Virtual Impedance Based Control to Enhance the Stability of Islanded Microgrid

Jiang Enyu,Zhao Jikang,Shi Zhengjing,Mi Yang,Lin Shunfu,Muyeen S. M. 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.5

This paper focuses on the voltage stability issue of an islanded microgrid in a cost-effective way adding the concept of adaptive virtual impedance. In the islanded microgrid structure, the mis-match of line impedance between the Distributed Generation (DG) units and imbalance of inverter local load are two critical factors to be dealt with carefully. These can result in serious circulating current and unreasonably reactive power sharing among DG units by using the conventional droop control method. In practical engineering, line inductance is often increased to eliminate the impedance mismatch. However, such a method would lead to an increase in cost, weight, and volume. To solve this problem, an adaptive virtual impedance droop control strategy based on fuzzy controller is proposed. Instead of DG units are equipped with series inductors, an adaptive virtual impedance is introduced to adaptively eliminate the reactive power error caused by the inconsistency of the line impedance through the fuzzy controller. At the same time, in order to deal with the droop control and the voltage drop at the inverter output caused by the addition of virtual impedance, a voltage compensation link is introduced to maintain the voltage within an acceptable range. The simulations were performed in Matlab/Simulink and RT-LAB experiments to verify the validity of the proposed control strategy.

Dual-layer Fuzzy Control Architecture for the CAS Rover Arm

Hongwei Gao,Yangmin Li,Jinguo Liu,Kun Hong,Yang Zhang 제어·로봇·시스템학회 2015 International Journal of Control, Automation, and Vol.13 No.5

Since the conventional impedance control method for a rover arm is not suitable for unconstructed environment with uncertainties, a fuzzy inference method which improves the impedance model dynamically is introduced to realize high-precision control. The fuzzy PD control algorithm which applies to the joint control of a rover arm is analyzed in this paper. With the two level control algorithms, a novel dual-layer fuzzy control framework is proposed, which can enhance the control performance significantly. In order to verify the validity and reliability of the designed algorithms, the robotic arm of the CAS rover is considered as an experimental platform. Kinematics and dynamics models of robotic arm are derived at first. Moreover, the fuzzy inference mechanism and implementation process of impedance model parameters are illustrated. Extensive simulations and experimental results show that the control accuracy and the force control of the system have been significantly improved with the proposed dual-layer fuzzy control architecture.

Modeling, Analysis, and Enhanced Control of Modular Multilevel Converters with Asymmetric Arm Impedance for HVDC Applications

Peng Dong,Jing Lyu,Xu Cai 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.6

Under the conventional control strategy, the asymmetry of arm impedances may result in the poor operating performance of modular multilevel converters (MMCs). For example, fundamental frequency oscillation and double frequency components may occur in the dc and ac sides, respectively; and submodule (SM) capacitor voltages among the arms may not be balanced. This study presents an enhanced control strategy to deal with these problems. A mathematical model of an MMC with asymmetric arm impedance is first established. The causes for the above phenomena are analyzed on the basis of the model. Subsequently, an enhanced current control with five integrated proportional integral resonant regulators is designed to protect the ac and dc terminal behavior of converters from asymmetric arm impedances. Furthermore, an enhanced capacitor voltage control is designed to balance the capacitor voltage among the arms with high efficiency and to decouple the ac side control, dc side control, and capacitor voltage balance control among the arms. The accuracy of the theoretical analysis and the effectiveness of the proposed enhanced control strategy are verified through simulation and experimental results.