Disturbance Observer Based Control System Research Articles

Frequency Response Data Based Disturbance Observer Design: With Application to a Nonminimum Phase Motion Stage

Disturbance observer based control system, which utilizes estimated disturbance to compensate the influence of real disturbance, is widely applied in industrial systems. In this article, a frequency response data based auto-tuning method is proposed to design a bandwidth-optimized disturbance observer. The identification of a nominal plant model and the design of a low-pass filter are accomplished simultaneously in the discrete domain. This significantly reduces the design effort required in existing parametric model-based and experience-based methods. A convex optimization problem is formulated by converting all the original constraints into convex form to save calculation time. Finally, the efficacy of the proposed method is verified by comparing the experimental results of existing methods with those of the proposed method in a nonminimum phase motion stage.

Analysis of disturbance observer-based control systems via spherical polynomials

Robustness analysis of disturbance observer (DOB)-based control systems under parametric uncertainty is addressed in this study. A spherical polynomial family-based approach is adopted to analyse how much uncertainty can be tolerated, and to capture a unified framework for different cases including non-minimum phase plant and different nominal and perturbed plant structures. Results are validated using the value set concept for spherical polynomial families. The study has shown that if the relative degrees of the perturbed plant and the nominal plant are equal, then robustness is achievable even if the plant model is low order. Although non-minimum phase zeros limit the selection of DOB bandwidth, the robustness margin can be exactly determined for a given DOB bandwidth. Furthermore, it is shown that when the plant numerator and denominator have uncertain parameters, the robustness margin is not increased as with the DOB filter bandwidth in general.

High Order Disturbance Observer Based PI-PI Control System With Tracking Anti-Windup Technique for Improvement of Transient Performance of PMSM

This paper focuses on designing a disturbance observer-based control (DOBC) system for PMSM drives. The cascade structure of the discrete-time PI-PI control system with tracking anti-windup scheme has been designed for both loops. In this study, high order disturbance observer (HODO) based control is used to improve the speed tracking performance of the control system for the PMSM prototyping kit regardless of the disturbance and unmodelled dynamics. The motion equation was modified in the HODO in which torque losses due to the drug resulting from the time-varying flux, hysteresis, and friction have been taken into account to estimate the total disturbance. The HODO does not require the derivatives of the disturbance to be zero, like in the traditional ones. It demonstrates its ability to estimate along with a load torque the high order disturbances caused by a cogging torque and a high-frequency electromagnetic noise in the PMSM system. In the real-time experiments, the proposed algorithm with HODO achieves less speed errors and faster response comparing with the baseline controller. The performances with proposed and baseline control have been evaluated under mechanical speed and load torque variation cases. The experimental results have proved the feasibility of the proposed control scheme. The proposed disturbance observer-based control system was implemented with a Lucas-Nuelle 300 W PMSM prototyping kit.

Design and Kinematics Analysis of a Robotic Pediatric Neuroendoscope Tool Body

Endoscopy is often used to treat hydrocephalus, a common pediatric neurosurgical condition. Rigid endoscopic tools used in these procedures have many limitations. In this article, we propose four novel designs for a steerable two degree-of-freedom robotic tool body to be deployed through a rigid endoscope and a handheld controller for such a tool body. Each of these designs make use of tendon-driven joints known as asymmetric notch joints, while varying tendon routing techniques. Furthermore, we design a compact handheld controller for this steerable tool body, which consists of dc motors driving lead screws to actuate the tendons for each of the robot's joints. A disturbance observer-based control system for these motors is designed to allow the motor to reach the desired tendon displacements under various loading conditions. Next, we analyze the kinematics of the bidirectional asymmetric notch joint, deriving a relationship between the joint angle and corresponding tendon displacement. Finally, we test each of our four proposed designs for interjoint coupling and provide some insights into the results of our tests. We find that tendon routing strategies play an important role in minimizing tendon coupling for meso-scale continuum tendon-driven robots and combining the properties of each of these asymmetric joints can prove to be beneficial in improving the performance of such two degree-of-freedom robots.

High performance motion control for optical satellite tracking systems

This paper investigates the motion control system of an optical telescope system used for precision satellite tracking and ranging applications. The system uses direct-drive permanent magnet synchronous motors (PMSMs) for high precision positioning. To overcome the performance limitations due to system dynamics and position dependent plant variations, a disturbance observer based control system is utilized. This paper contributes the detailed analysis, design and implementation of such an advanced control concept for the performance improvement of precision satellite tracking systems. Satellite tracking experiments are conducted to verify the performance of the proposed system. Utilizing the proposed control concept, the RMS servo error is reduced by a factor of 3.8 to well below the arcsecond range, achieving seeing limited tracking.

Real-time Inverse Model Estimation by a Recursive Least Squares Method for Disturbance Observer-based Control Systems: Balancing Control of a Single-wheel Robot

This article proposes a real-time identification and control technique for disturbance observer (DOB) - based control systems to improve the balancing control performance of a single-wheel robot. In a DOB-based control configuration, the inverse model of the system is obtained by inverting the identified forward model to extract the disturbance. However, a problem arises when the stability of the inverse model is not guaranteed. The Q filter design may solve the problem, but the process is time consuming. Therefore, we propose a stable inverse model identification technique with a minimal effort of designing Q filters in DOB schemes. The proposed scheme follows three steps: a recursive least square (RLS) method is used for updating the parameters of a second order model. Then the stability is checked. The last step is to make the model stabilized depending upon the stability through the all-pass-filter technique. After these steps, the transformed inverse model becomes stable and finally can be used for DOB control schemes. Experimental studies on balancing control of a single-wheel robot are conducted and their performances are compared to verify the proposal.

Iteration Tuning of Disturbance Observer-Based Control System Satisfying Robustness Index for FOPTD Processes

A conventional disturbance observer (DOB)-based control system is a model-based control system. In this paper, a data-driven design method is proposed for the DOB-based control system using iteration feedback tuning (IFT) based on the first-order-plus-time-delay models. It is well known that the conventional data-based design methods cannot provide an explicit tradeoff between robustness and performance. Here, our goal is to develop a method to design the data-driven DOB-based control system satisfying a given robustness index. To this end, first, the tuning rules of the controller and the $Q$ -filter in terms of the nominal process model are analytically determined for a given robustness index. Second, an optimization problem, solved by IFT algorithm, is established to find the optimal parameters of the nominal model. The merits of the proposed method are that: 1) the number of parameters needing to be tuned is reduced, since only the parameters of the nominal model are optimized and 2) the system satisfies the explicit robustness index if the parameters are optimal. Moreover, the selection of the robustness index, the output performance of the system, and the performance of the iteration algorithm are addressed. Two simulation examples and an experiment are presented to demonstrate the effectiveness and merits of the proposed method.

Analysis the robustness of control systems based on disturbance observer

Disturbance observer (DOB) estimates the system disturbances by using the inverse of the nominal plant model and a low pass filter (LPF). Although the LPF provides the properness in the inner-loop, it is the main design constraint of the control systems based on DOB. The bandwidth of the LPF is designed as high as possible so that the DOB can estimate the disturbances in a wider frequency range. However, its bandwidth is limited by noise and robustness of the system. The robustness limitation is directly related with the robustness analysis methods, and they significantly affect the performance of the DOB based control systems. In this paper, three different robustness analysis methods are implemented into the DOB based control systems, and the relation between the robustness of the system and bandwidth of DOB is clearly explained. The conservatism, which is the main drawback of the conventional analysis methods, on the bandwidth of DOB is removed by proposing a new real parametric uncertainty based analysis method. The proposed methods are compared in detail, and simulation results are given to show the validation.

Nominal model manipulation for enhancement of stability robustness for disturbance observer-based control systems

Disturbance observer-based control systems often encounter the stability problem due to modeling uncertainties. In such cases, the disturbance observer (DOB) may have to be re-designed by narrowing the bandwidth of the Q-filter to enhance stability robustness, but this approach to stability enhancement deteriorates the performance of DOB. In order to improve robust stability while maintaining the performance of DOB, this paper proposes a method that manipulates the nominal plant model in the DOB; the parameters of the discretized nominal model are optimized to improve robust stability in the discrete time domain. For the optimization of nominal model, it is assumed that the closed-loop poles of DOB are subjected to multiplicative uncertainties, and the maximum allowable magnitude of uncertainties is utilized as the measure of stability robustness. Then, the proposed method changes the location of closed-loop poles to maximize the robustness margin. This paper provides a case study that includes experimental results.

Electric wheelchair control with gaze direction and eye blinking

We propose an electric wheelchair controlled by gaze direction and eye blinking. A camera is set up in front of a wheelchair user to capture image information. The sequential captured image is interpreted to obtain the gaze direction and eye blinking properties. The gaze direction is expressed by the horizontal angle of the gaze, and this is derived from the triangle formed by the centers of the eyes and the nose. The gaze direction and eye blinking are used to provide direction and timing commands, respectively. The direction command relates to the direction of movement of the electric wheelchair, and the timing command relates to the time when the wheelchair should move. The timing command with an eye blinking mechanism is designed to generate ready, backward movement, and stop commands for the electric wheelchair. Furthermore, to move at a certain velocity, the electric wheelchair also receives a velocity command as well as the direction and timing commands. The disturbance observer-based control system is used to control the direction and velocity. For safety purposes, an emergency stop is generated when the electric wheelchair user does not focus their gaze consistently in any direction for a specifi ed time. A number of simulations and experiments were conducted with the electric wheelchair in a laboratory environment.