Discrete-time sliding mode control of a direct-drive robot manipulator

This paper investigates application of a recently introduced discrete-time sliding mode algorithm, in robot motion control. This algorithm was developed to ensure chattering-free discrete-time sliding mode control in finite time. Robustness against disturbances and modeling errors are the additional merits of this algorithm. Here, the algorithm is adapted for the robot motion control problem, and it is used to design feedback controllers of a benchmark direct-drive robot. Theory and experiments confirm the applicability of the algorithm. However, they also reveal restrictions in controller tuning, that may result in undesirable amplification of noise and in excitation of parasitic dynamics

Sliding mode control with system constraints for aircraft engines

This paper proposes a constraint-tolerant design with sliding mode strategy to improve the stability of aircraft engine control. To handle the difficulties associated with the high-frequency switching laws, merely attenuating the chattering is far from satisfactory. System constraints on input, output, and input rate should be addressed in the design process. For a sort of uncertain nonlinear systems subjected to the constraints, sliding mode regulators are designed using Lyapunov analysis. A turbofan engine is adopted for simulation, which shows that the methodology developed in this paper can handle the speed tracking and limit protection problem in a stable fashion, despite the negative influence posed by the system constraints

Design of a Memristor-based Chattering Free Sliding Mode Controller and Speed Control of the BLDC Motor

In this study, a memristor-based sliding mode controller (Mem-SMC) was designed for speed control of BLDC motor and the performance of the controller was tested in simulation. The sliding mode controller, known for its robustness against disturbances and parameter variations, was designed with a memristor known as a missing circuit element. Simulation results show that the proposed controller is successful in the speed reference tracking and is also able to respond quickly to sudden changes in the reference

Local and global controllers for decentralized discrete-time variable structure control technique for large-scale systems

This thesis presents a research on new discrete-time integral variable structure controllers for large-scale systems in the presence of matched and unmatched uncertainties. It is found in the literatures that limited works have been done on variable structure control for discrete-time large-scale system. Current computer technology allows direct implementation of discrete-time controller to control a system with greater simplicity and cost saving. The controllers developed in this research are able to achieve system stability in terms of both global and local controls. A global controller makes use of feedback from all subsystems to achieve the quasi-sliding surface and remains on it, with better performance than local controller. A local controller is able to perform the controlling task with feedback solely from the local subsystem itself, with simpler design but is compromised in performance. New theorems with mathematical proof for both local and global controllers are presented and simulations are carried out using Matlab for three different types of large-scale systems to test the proposed controllers. The simulation results also showed that the global controller has better performance than the local controller. Discrete-time integral variable structure control lets the implementation of the controller for large-scale systems a much more straight forward approach with computer. Furthermore, the characteristic of robustness in variable structure control ensures systems fast convergence to the desired value and rejects uncertainties and disturbances, which makes it very practical to be applied to many large-scale systems in real world applications. These newly developed controllers are able to provide cost effective implementations of discrete-time variable structure controllers using current digital hardware for various large-scale plants such as petrochemical, traffic control, telecommunication and robotic system

Global Gain Outer Loop Method for Discrete-time Sliding Mode Control

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2021. 2. 조동일.본 논문에서는 이산 시간 슬라이딩 모드 제어 방법(discrete-time sliding mode control, DSMC) 및 외란 보상기(decoupled disturbance compensator, DDC)에 적용할 수 있는 전역 이득 외부 루프 방법(global gain outer loop method)을 분석하였다. 기존 DSMC 방법은 위치추종 성능이 좋고 외란에 대해 강인하며, 구현이 쉬워 다양한 제어환경에 널리 적용되고 있다. 또한 DSMC와 DDC를 함께 사용하여 느리게 변화하는 외란에 대해 강인함을 부여하는 연구가 진행되었다. 하지만 산업용 서보 시스템에서 위치 제어를 수행할 때, 램프 함수 형태의 외란이 인가될 경우 위치 오차가 0으로 수렴하지 못하는 문제가 발생한다. 본 논문에서는 램프 함수 형태의 외란이 있는 시스템에서 레퍼런스 입력을 재생성하여 정상상태 위치 에러를 0으로 수렴시키는 전역 이득 외부 루프 방법을 제안한다. 또한 제안한 방법은 제어 입력 포화(control input saturation)를 억제하는 효과를 갖는 보조상태변수(auxiliary state)기법과 함께 사용될 수 있음을 보인다. 특히 보조상태변수의 게인을 1로 설정할 경우, 목표 위치에서 추가적인 진동 없이 잘 제어가 됨을 보인다. 전역 이득 외부 루프 방법을 DSMC+DDC 방법에 적용할 때 최종값 정리를 이용하여 램프 함수 외란과 제어 입력 포화 이후에 위치 에러가 0이 되는 것을 보인다. 실제 산업용 서보 시스템에 제어기를 구현하여 제안하는 방법이 목표 위치에서 오버슈트를 줄이고 제어 성능을 향상시킴을 보였다.This paper presents a global gain outer loop method for discrete-time sliding mode control (DSMC) with a decoupled disturbance compensator (DDC). The original DSMC method is widely used in theoretical areas and industrial applications attributed to its excellent properties of trajectory tracking, robustness to disturbances and easy implementation. DSMC with DDC was developed to maintain closed-loop stability subject to slowly-varying disturbances. However, when the system suffers from ramp-type disturbance in position control application, overshoot arises at the end of motion. In this paper, a global gain outer loop method is proposed which regenerates the reference input and guarantees asymptotic convergence of the error state in the presence of ramp-type disturbance. Moreover, the developed method can be utilized with an auxiliary state method which is effective to maintain stability under control input saturation. Especially, we can set the gain of auxiliary state to 1 to suppress additional vibration at the end of motion. Final-value theorem is utilized to demonstrate the effectiveness of the proposed method. Experiments are performed on a servo system to demonstrate the improved overshoot performance.제 1 장 서 론 1 제 1.1 절 연구의 배경 1 제 1.2 절 연구의 구성 7 제 2 장 산업용 서보 시스템의 분석 8 제 2.1 절 플랜트 8 제 2.2 절 제어기 및 필터 10 제 3 장 전역 이득 외부 루프 방법 12 제 3.1 절 기존 DSMC+DDC 제어기 12 제 3.2 절 외부 루프를 추가한 DSMC+DDC 제어기 18 제 3.3 절 실험 결과 23 제 4 장 제어 입력 포화 상에서의 분석 30 제 4.1 절 기존 보조상태변수 방법 30 제 4.2 절 보조상태변수와 전역 이득 외부 루프 방법 34 제 4.3 절 실험 결과 37 제 5 장 결 론 41 참고문헌 42 Abstract 47 감사의 글 49Maste

Robust Position-based Visual Servoing of Industrial Robots

Recently, the researchers have tried to use dynamic pose correction methods to improve the accuracy of industrial robots. The application of dynamic path tracking aims at adjusting the end-effector’s pose by using a photogrammetry sensor and eye-to-hand PBVS scheme. In this study, the research aims to enhance the accuracy of industrial robot by designing a chattering-free digital sliding mode controller integrated with a novel adaptive robust Kalman filter (ARKF) validated on Puma 560 model on simulation. This study includes Gaussian noise generation, pose estimation, design of adaptive robust Kalman filter, and design of chattering-free sliding mode controller. The designed control strategy has been validated and compared with other control strategies in Matlab 2018a Simulink on a 64bits PC computer. The main contributions of the research work are summarized as follows. First, the noise removal in the pose estimation is carried out by the novel ARKF. The proposed ARKF deals with experimental noise generated from photogrammetry observation sensor C-track 780. It exploits the advantages of adaptive estimation method for states noise covariance (Q), least square identification for measurement noise covariance (R) and a robust mechanism for state variables error covariance (P). The Gaussian noise generation is based on the collected data from the C-track when the robot is in a stationary status. A novel method for estimating covariance matrix R considering both effects of the velocity and pose is suggested. Next, a robust PBVS approach for industrial robots based on fast discrete sliding mode controller (FDSMC) and ARKF is proposed. The FDSMC takes advantage of a nonlinear reaching law which results in faster and more accurate trajectory tracking compared to standard DSMC. Substituting the switching function with a continuous nonlinear reaching law leads to a continuous output and thus eliminating the chattering. Additionally, the sliding surface dynamics is considered to be a nonlinear one, which results in increasing the convergence speed and accuracy. Finally, the analysis techniques related to various types of sliding mode controller have been used for comparison. Also, the kinematic and dynamic models with revolutionary joints for Puma 560 are built for simulation validation. Based on the computed indicators results, it is proven that after tuning the parameters of designed controller, the chattering-free FDSMC integrated with ARKF can essentially reduce the effect of uncertainties on robot dynamic model and improve the tracking accuracy of the 6 degree-of-freedom (DOF) robot

Chattering-free discrete-time sliding mode control

To avoid the chattering problem in the reaching-law-based discrete-time sliding mode control (DSMC) and the generation of over-large control action in the equivalent-control-based DSMC, a new DSMC method based on non-smooth control is proposed in this paper. Since there is no use of any switching term in the proposed DSMC, it is a chattering-free SMC method. Meanwhile, it is shown that the newly proposed non-smooth control-based DSMC can guarantee the same level of accuracy for the sliding mode motion as that of an equivalent control-based DSMC. To demonstrate the effectiveness of the proposed approach, a simulation example is presented

Development of U-model enhanced nonlinear dynamic control systems —Framework, algorithms and validation

This study aims to develop the classical model-based U-control design framework to enhance its robustness and reduce its dependence on model accuracy. By absorbing the design concepts of other advanced control algorithms, firstly, based on the discrete-time U-control algorithm, a continuous-time (CT) U-model based dynamic inversion algorithm is proposed. Then the CT U-control system design procedures are presented and explained step by step with numerical and simulation demonstrations of the linear and nonlinear U-control system design examples. Secondly, the U-control algorithm develops two mainstream nonlinear robust control algorithms, disturbances suppression and disturbances compensation, while maintaining its system dynamic cancellation characteristics, including two-degree-of-freedom U-model-based internal model control (UTDF-IMC), Disturbance observer-based U-control (DOBUC), sliding mode enhanced U-control (U-SMC) and U-model based double sliding mode control (UDSMC) algorithms. At the same time this study first developed and applied the U-control method to a practical industry application: robust quadrotor trajectory tracking control. The proposed UDSMC method and multiple-input and multiple-output extended-state-observer (MIMO-ESO) established the quadrotor flight control system. The difficulties associated with quadrotor velocity measurement disturbances and uncertain aerodynamics are successfully addressed in this control design. A rigorous theoretical analysis has been carried out to determine whether the proposed control system can achieve stable trajectory tracking performance, and a comparative real-time experimental study has also been carried out to verify the better effectiveness of the proposed control system than the classical SMC and built-in PID control system. This study is clearly novel as the methods and experiments it proposed have not been researched before