Sliding Perturbation Observer Research Articles

Perturbation Observer-Based Obstacle Detection and Its Avoidance Using Artificial Potential Field in the Unstructured Environment

Different methodologies for manipulators have been proposed and applied to robot obstacle detection and avoidance in unstructured environments. These methods include different real-time sensors, observer-based algorithms, and path planning using genetic algorithms. However, sensor design integration is complex and considerably expensive. Moreover, the observer algorithm requires complete system dynamics information, which is difficult to derive. In this regard, genetic algorithms are typically considered slow and difficult to optimize. Accordingly, this study proposes a sensor-less obstacle detection technique using a nonlinear observer (known as sliding perturbation observer (SPO)). Obstacle avoidance is also implemented using a motion planner (known as artificial potential field (APF)). The SPO is a nonlinear observer that only requires the partial position and provides all other states (such as position, velocity) and perturbation (non-linearities and external disturbance). The SPO estimates the external torque at each joint resulting from contact (i.e., collision) with an obstacle. Obstacles are detected and avoided by integrating the SPO and APF. The estimated external torque detects the obstacle location and a repulsive force from the APF is applied to avoid this obstacle. To achieve obstacle avoidance, the sum of all estimated torques must be zero. The proposed technique is applied to a robot manipulator with five degrees of freedom.

Fuzzy TSMCSPO for Trajectory Tracking of Nuclear Reactor Dismantlement Robot Manipulator

In this study, a fuzzy logic system to tune the parameters of terminal sliding mode control with a sliding perturbation observer (TSMCSPO) in real-time is proposed according to the system’s state changes to improve the control performance of TSMCSPO for a 5-DOF robot manipulator used for nuclear reactor dismantlement. Accurate trajectory tracking control is required when using a multi-DOF robot manipulator to cut the decommissioned nuclear reactor. A TSMCSPO scheme using TSMC in SPO has been proposed in previous research, which improves the estimation and convergence performance of traditional SMCSPO. In TSMCSPO, the parameters of the controller are important to enhance the control performance. Moreover, due to the influence of the working environment and the uncertainty of the system, the characteristics of the system will be changed during the trajectory tracking control of the multi-degree-of-freedom robot manipulator. Therefore, real-time optimal parameter tuning is required. In this regard, using fuzzy logic to tune the parameters is an effective method. By designing fuzzy rules, the controller parameters can be optimized. In this study, the proposed algorithm and, the trajectory tracking control simulation of the robot manipulator in the nuclear reactor vessel internal (RVI) are implemented in MATLAB/Simulink environment. The control algorithm is verified by the experiments on a real robot manipulator platform. The outstanding control performance of the algorithm is demonstrated by comparing the trajectory tracking error between the proposed fuzzy TSMCSPO scheme and TSMCSPO with fixed parameters.

Nonsingular terminal sliding mode control with sliding perturbation observer for a permanent-magnet spherical actuator

In order to deal with the modeling of uncertainty and external environment disturbance in the trajectory tracking system of 3 degrees of freedom permanent-magnet spherical actuator, a nonsingular terminal sliding mode control method with sliding perturbation observer is proposed in this article. First, a sliding perturbation observer, which can estimate compound disturbance only by feedback position signals, is proposed to reduce the uncertainty caused by angular velocity observation. Then, based on the sliding perturbation observer, a nonsingular terminal sliding mode control method is designed to satisfy the requirements of system nonsingularity, robustness, and control accuracy. The stability of the controller is proved by the Lyapunov theory. Finally, simulation and experimental results show that the proposed control method has excellent anti-disturbance performance, which provides an important reference for the future applications of permanent-magnet spherical actuators in aerospace and other industrial fields.

Force/Torque-Based Impedance Control With Perturbation Observer—Toward High Payload System Robust Trajectory Tracking

This paper presents a robust force/torque-based impedance control that reacts to deviated motion by generating forces to achieve the desired impedance, particularly for high payload systems. One of the special cases of such systems is an assistive robot for paraplegics (ARP) with a sit-stand mechanism (STSM) and, therefore, its control is investigated. Recently, a nonlinear robust position control known as sliding mode control with sliding perturbation observer (SMCSPO) was implemented on STSM and proven its effectiveness. However, with increasing subject body mass, high switching control gains are required which consequently either result in increased tracking error or chattering in control performance. In this regard, a new framework of integrated control was proposed which combines the feature of impedance control with estimated information from SMCSPO resulting in an enhanced control algorithm. The advantage of this impedance control is that because of SMCSPO, it utilizes the linear system information with position feedback only to estimate the states and perturbation (nonlinearities, uncertainties, and disturbance). This estimated perturbation then helps in compensating the actual perturbation effect from the system response. Moreover, the impedance control excludes the saturation function which helps prevent the chattering with low control gains. The comparison simulation and experiment results of the proposed impedance control with SMCSPO validated the proposed algorithm which enhances the transient response with minimized estimation error and better perturbation estimation.

Robust Control Design for Accurate Trajectory Tracking of Multi-Degree-of-Freedom Robot Manipulator in Virtual Simulator

Robot manipulators have complex dynamics and are affected by significant uncertainties and external disturbances (perturbations). Consequently, determining the exact mathematical model of a robot manipulator is a tedious task. Accordingly, accurate trajectory tracking is a dominant feature in the design of position control for robot manipulators. The main objective of this research is to design a robust and accurate position control for a robot manipulator despite the absence of an exact model. For this purpose, an extended state observer (ESO)-based sliding mode control (SMC) is proposed. The main concept in the ESO is to define and estimate the assumed perturbation, which includes known and unknown system dynamics, uncertainties, and external disturbances. Additionally, the ESO estimates the system states. This estimated perturbation information, which is combined with the SMC input, is utilized as a feedback term to compensate for the effect of the actual perturbation. The perturbation compensation improves the controller performance, resulting in a slight position error, less sensitivity to perturbation, and a small switching gain required for the SMC. The advantage of the proposed algorithm is that it only requires partial state information and position feedback. Thus, identifying the system parameters for the nominal model before designing the controller is unnecessary. The proposed algorithm is implemented and compared with the conventional SMC and the SMC with a sliding perturbation observer (SMCSPO) in a virtual environment based on MATLAB SimMechanics. The comparison results validate the robustness of the proposed technique in the presence of perturbation and show that the technique has a significantly reduced trajectory tracking error than the conventional SMC and SMCSPO.

SMCSPO-Based Robust Control of AUV in Underwater Environments including Disturbances

In the underwater environment, robust control algorithms are required to control autonomous underwater vehicles (AUVs) at high speed while preventing large nonlinearities and disturbances. Sliding mode control (SMC) is a well-known robust control theory and has been widely used not only in AUV control but also in systems such as industrial robots which have high nonlinearity in their system dynamics. However, SMC has the disadvantage of causing chattering on the control input, and it is difficult to apply this method to the control fins of an AUV system that cannot move its fins at high speed underwater. In this work, a design for a sliding mode control with sliding perturbation observer (SMCSPO) algorithm is applied to AUVs, and the simulation results under underwater disturbance conditions are discussed. From simulation using MATLAB, it is confirmed that AUV control using SMCSPO shows better trajectory tracking control performance without chattering than PID control.

Robust Controller for Pursuing Trajectory and Force Estimations of a Bilateral Tele-Operated Hydraulic Manipulator

In hazardous/emergency situations, public safety is of the utmost concern. In areas where human access is not possible or is restricted due to hazardous situations, a system or robot that can be distantly controlled is mandatory. There are many applications in which force cannot be applied directly while using physical sensors. Therefore, in this research, a robust controller for pursuing trajectory and force estimations while deprived of any signals or sensors for bilateral tele-operation of a hydraulic manipulator is suggested to handle these hazardous, emergency circumstances. A terminal sliding control with a sliding perturbation observer (TSMCSPO) is considered as the robust controller for a coupled leader and hydraulic follower system. The ultimate use of this controller is as a sliding perturbation observer (SPO) that can estimate the reaction force without any physical force sensors. Robust and perfect position tracking is attained with terminal sliding mode control (TSMC) in addition to control of the hydraulic follower manipulator. The force estimation and pursuing trajectory for the leader–follower system is built upon a bilateral tele-operation control approach. The difference between the reaction forces (caused by the remote environment) and the operating forces (applied by the human operator) required the involvement of an impedance model. The impedance model is implemented in the leader manipulator to provide human operators with an actual sense of the reaction force while the manipulator connects with the remote environment. A camera is used to ensure the safety of the workplace through visual feedback. The experimental results showed that the controller was robust at pursuing trajectory and force estimations for the bilateral tele-operation control of a hydraulic manipulator.

Trajectory Tracking Control of Multi-DOF Robot without Considering System Dynamics

In this study, two different control logics have been designed for the position control of a robot with five degrees of freedom (DOFs). First, a sliding mode control with a sliding perturbation observer (SMCSPO) has been proposed. The SMCSPO is robust against perturbation, which is the sum of nonlinearities, parametric uncertainties, and external disturbances. To implement the SMCSPO, linear parameters of the system are required; however, these are difficult to identify. Moreover, it is exigent to derive the equation of motion for the multi-DOF robot. Accordingly, an integral sliding mode control (ISMC) has been designed for the position control of this multi-DOF robot. The ISMC controller does not require a mathematical model of the system. The ISMC control input applies a switching gain to compensate for the perturbation and system dynamics. In comparison with the SMCSPO, the ISMC has improved the tracking performance of the system because of its unique characteristics. Both control schemes have been implemented in MATLAB/Simulink. It has been observed that the tracking error of each ISMC joint is lower than that of the SMCSPO.

Fast Fractional-Order Terminal Sliding Mode Control With RBFNN Based Sliding Perturbation Observer for 7-DOF Robot Manipulator

A new perturbation estimator, using radial basis function (RBF) neural networks (RBFNN) to modify the sliding perturbation observer (SPO), is proposed with the fast fractional-order terminal sliding mode control (FFOTSMC). It aims to control a seven-degree-of-freedom (7-DOF) robot manipulator. The new perturbation estimator applies the data-driven method RBFNN to compensate for the estimation error in the conventional SPO for the first time. The modified SPO estimates the perturbation, which contains the disturbance, dynamic uncertainties, and modeling errors. The estimated perturbation is used to design with the FFOTSMC, which improves the tracking accuracy and reduces the chattering. The FFOTSMC was designed using the fractional-order derivative to design the sliding surface and the reaching/law for reaching the sliding surface. In experiments on the robot, the proposed estimation method has been evaluated by comparing with the conventional SPO or only RBFNN with the same controller, FFOTSMC. The asymptotic stability of the controller with the new estimator is proved using Lyapunov functions for fractional-order systems.

Control of an Assistive Robot for Paraplegics Using PID Controller with Sliding Perturbation Observer

Control of an Assistive Robot for Paraplegics Using PID Controller with Sliding Perturbation Observer

Fast Fractional-Order Terminal Sliding Mode Control for Seven-Axis Robot Manipulator

This paper proposes a novel controller, fast fractional-order terminal sliding mode control (FFOTSMC), for a seven-degree-of-freedom (7-DOF) robot manipulator with tracking control. The new controller applies the fractional-order derivative on both the sliding surface design and the sliding control/reaching law. Compared to previous research, which only applies the fractional-order derivative on the sliding surface design, the proposed controller has a faster convergence for reaching the sliding surface and maintaining stay on it because of the new fractional-order control law, which helps the tracking accuracy. To implement the controller on the robot with less chattering, a sliding perturbation observer (SPO) is used to estimate the disturbance and uncertainties. Stability analysis is analyzed using Lyapunov functions for fractional-order systems. The controller performance is evaluated by a simulation of a single-input and single-output (SISO) system in MATLAB Simulink and experiments on the robot manipulator.

Evaluation of Force Estimation Method Based on Sliding Perturbation Observer for Dual-arm Robot System

Dual-arm robots require information on the end-effector’s assembly force for the precision and accuracy of assembly work to be ensured. However, the attachment of a force sensor to the end-effector not only considerably increases cost and weight but also introduces structural problems. In this study, through simulations and experiments, a sliding perturbation observer is applied to a seven-degree-of-freedom robot arm to estimate the assembly force without the use of a force sensor. This paper proposes a method for determining whether the end-effector of a robot arm collides with an assembly part on the basis of the estimated perturbation without a force sensor. If the absolute values of the axes perturbations sharply increase, then it can be assumed that the end-effector of the robot manipulator and the assembly part have collided. This research also evaluates the extent of similarity between the estimated perturbation and reaction force at the moment of assembly.

Trajectory Tracking Control Using Fractional-Order Terminal Sliding Mode Control With Sliding Perturbation Observer for a 7-DOF Robot Manipulator

A novel control scheme utilizing fractional-order terminal sliding mode control with sliding perturbation observer (FOTSMCSPO) is proposed herein. It was used to solve the trajectory tracking problem on a seven-degree-of-freedom robot manipulator. The fractional-order terminal sliding mode in FOTSMCSPO provides a finite convergence time for reaching the sliding surface. In this article, a sliding perturbation observer (SPO) is used to estimate the disturbance from the environment and modeling uncertainties. The new control scheme exhibits high precision, fast convergence, and robust performance against the lumped uncertainties. These advantages are ensured through the newly designed fractional-order terminal sliding surface and the SPO. The stability is analyzed based on the Lyapunov functions for general and fractional-order systems. An implementation on a real robot manipulator demonstrated the effects and performance of the new control method.

Tele-Operated Bilateral Control of Hydraulic Manipulator Using a Robust Controller Based on the Sensorless Estimated Reaction Force

In nuclear power plants (NPP), dismantling is the most technically involved process during their life time. During the dismantling process, public safety must be ensured. In crisis situations, a remotely controlled robot system is needed for the dismantling of NPP. Therefore, in this research, a bilateral tele-operation system is proposed to tackle these emergency conditions. Transparency can be improved by using force and position signal in the control strategy. In some applications, force cannot be determine directly using physical sensors. In this work, a novel tele-operated bilateral control strategy is proposed to estimate the reaction force of 3-degree-of-freedom (DOF) master and hydraulic slave manipulators without the use of a sensor. The control strategy is developed by using sliding mode control with sliding perturbation observer (SMCSPO). The sliding perturbation observer (SPO) estimates the reaction force at the end effector and second link without using sensors. The sliding mode control (SMC) is used as a tele-operated bilateral controller for the robust position tracking and control of the slave device. The impedance model is used to differentiate between the applied force (force exerted by operator) and the reaction force due to the remote environment. Different experiments were performed to verify the proposed strategy. The results indicate that the slave manipulator exactly follows the trajectory of the master device. A camera is used to take visual feedback of the workspace for safety purpose. This technique can also be applied for higher-order DOF manipulators in NPP.

Trajectory Tracking Control of a Hydraulic System Using TSMCSPO based on Sliding Perturbation Observer

This paper proposes a new designed trajectory tracking method for a hydraulic manipulator, which is the terminal sliding mode control with sliding perturbation observer (TSMCSPO). The dynamics of the hydraulic system are complex and uncertain, it also generates a large reaction force when working as an excavator or a dismantling robot. In this paper, the new control law is designed to force the trajectory of the hydraulic system to follow the reference despite complex dynamics, modeling error, the huge reaction force, and dynamic uncertainties. The sliding perturbation observer (SPO) in TSMCSPO estimates all disturbances from the outside environment, dynamic uncertainties, and modeling errors in real time. We included a simulation and an experiment to verify the approach, and to demonstrate the performance compared with other controllers (SMCSPO, SMC, and TSMC). Stabilities of SPO and TSMCSPO were analyzed based on the Lyapunov stability theory.

Efficient Control of a Non-Linear System Using a Modified Sliding Mode Control

Trajectory tracking is an essential requirement in robot manipulator movement and localization applications. It is a current research topic of interest, and several researchers have proposed different schemes to achieve the task accurately. This research proposes efficient control of a hydraulic non-linear robot manipulator using a modified sliding mode control, named proportional derivative sliding mode control with sliding perturbation observer (PDSMCSPO), to overcome parameter uncertainties and non-linearity. The proposed new control strategy achieves higher accuracy and better time convergence than the previous one. A positive derivative gain, which has a value less than one, is multiplied with the velocity error term of the sliding surface. The proposed control (PDSMCSPO) also achieves robustness. Results show that by introducing the derivative gain, the chattering from the system has been reduced more than classical sliding mode control (SMC). The reason is that during reaching phase this small gain multiplies with the perturbation and minimizes the effect of perturbation on the system. A smaller value of switching gain K is required as compared to SMC, and the transfer function between sliding surface and perturbation in proportional derivative sliding mode control (PDSMC)has low pass filter characteristics. The proposed PDSMCSPO has a faster response than previous sliding mode control with sliding perturbation observer (SMCSPO), and the output and sliding surface convergence to the desired value is much quicker than conventional logic. Some other characteristics such as error in the output are small because of more attenuation of the perturbation signal. Simulation and experimental results are presented for a link between the hydraulic robot manipulator and the mass damper system.

Implementation of a TSMCSPO Controller on a 3-DOF Hydraulic Manipulator for Position Tracking and Sensor-Less Force Estimation

In this study, a three-degree-of-freedom hydraulic system device configured as a master-and-slave manipulator system is considered. A methodology to estimate reaction force in aforementioned system is proposed without utilizing any force sensor/signal. A terminal sliding control with a sliding perturbation observer (TSMCSPO) is designed for coupled master-slave system. The fundamental benefit of the proposed scheme is that the sliding perturbation observer estimates the reaction force related to the end effector and second link without utilizing a force sensor. Robust and accurate position tracking is achieved with terminal sliding-mode control in addition to control of the slave manipulator. The position and force tracking for master-slave is estimated based upon bilateral control strategy. The difference in the reaction and operating force is included in the impedance model. The impedance model is implemented in the master device to provide the operator with a sense of the reaction force when it connects with the environment. The experimental results confirm the robust position and force tracking of the slave manipulator.

Estimated Reaction Force-Based Bilateral Control between 3DOF Master and Hydraulic Slave Manipulators for Dismantlement

This paper proposes a novel bilateral control design based on an estimated reaction force without a force sensor for a three-degree of freedom hydraulic servo system with master–slave manipulators. The proposed method is based upon sliding mode control with sliding perturbation observer (SMCSPO) using a bilateral control environment. The sliding perturbation observer (SPO) estimates the reaction force at the end effector and second link without using any sensors. The sliding mode control (SMC) is used as a bilateral controller for the robust position tracking and control of the slave device. A bilateral control strategy in a hydraulic servo system provides robust position and force tracking between master and slave. The difference between the reaction force of the slave produced by the effect of the remote environment and the operating force applied to the master by the operator is expressed in the target impedance model. The impedance model is applied to the master and allows the operator to feel the reaction force from the environment. This research experimentally verifies that the slave device can follow the trajectory of the master device using the proposed bilateral control strategy based on the estimated reaction force. This technique will be convenient for three or more degree of freedom (DOF) hydraulic servo systems used in dismantling nuclear power plants. It is worthy to mention that a camera is used for visual feedback on the safety of the environment and workspace.

Sensorless Reaction Force Estimation of the End Effector of a Dual-arm Robot Manipulator Using Sliding Mode Control with a Sliding Perturbation Observer

We estimated the reaction force for assembly work with a three-link dual-arm robot manipulator using sliding mode control with a sliding perturbation observer (SMCSPO) without using a force sensor. The sliding perturbation observer (SPO) is used to estimate the reaction force of the end effector without using any sensor. The SPO estimates the perturbation, which consists of the parameter uncertainties, nonlinear terms, and disturbances such as the reaction force. During assembly, the most effective perturbation term is close to the reaction force, so we assumed that the estimated perturbation is the same as the reaction force. The estimated perturbation was compared with the reaction force from the dynamics of the manipulator using a simulation with the SimMechanics toolbox of MATLAB/SIMULINK. The simulation results show the performance of the SMCSPO and that the reaction force can be estimated using the SPO without any sensor. The method can improve the structural reduction of link manipulator robots and decrease costs.

Terminal Sliding Mode Control with Sliding Perturbation Observer for a Hydraulic Robot Manipulator

Abstract A new design approach of sliding mode control with terminal sliding mode and sliding perturbation observer for a hydraulic robot manipulator is described in this paper. A sliding perturbation observer can observe the unknown states and disturbance. The estimated states and perturbation are used in sliding mode for more accuracy tracking. However, it occurs some time delay when use the combined controller. Terminal sliding surface can drive the system tracking error to origin with as faster speed than conventional one. Thus, terminal sliding mode control with sliding perturbation observer is designed with both fast convergence speed and high precision. In this paper, the experiment result demonstrate that.