Papers by Keyword: Disturbance Observer

Abstract: Our study aims to develop a small handy low-cost viscometer for nursing care food management. There are many methods to measure the viscosity of a fluid. In this research, the rotational viscometer employing the observer-based method instead of the actual torque transducer has been developed. The digitally controlled motor has been used to estimate the viscosity in real time with high accuracy. In order to verify the effectiveness of the developed viscosity estimation method, a prototype viscometer has been constructed and tested the viscosity estimation accuracy with standard liquids. As a result, the viscosity accuracy is equivalent to that of the conventional torque transducer-equipped viscometer.

Abstract: According to the characteristics of the electro-hydraulic position servo system of asymmetric hydraulic cylinder controlled by symmetric valve and its performance requirements, the PID controller based on disturbance observer is introduced. The improved controller can observe the equivalent disturbances and introduce the equivalent compensation to the control system, so it can achieve suppression of disturbance. In the MATLAB Simulink environment, the simulation results show that the controller has the very good quick response, the stronger robustness and the higher tracking precision.

Abstract: The cutting force is widely regarded as being the most valuable information when observing a metal cutting process. Considering practicability, indirect cutting force measurement methods which forego additional sensors have been studied in academic field. Disturbance observer-based cutting force estimation method was known as a typical example, and its validity was verified in linear motor driven stage. However, accurate cutting force estimation is still difficult in ball-screw driven stage because of non-linear friction and resonance. In this study, feasibility of sensorless cutting force estimation was verified by using large scale commercial machine tool. Considering that the motion of rotational and translational elements independently, cutting force observer (CFOB) was modeled as two-degree-of-freedom system. The CFOB was mounted to control systems of both stage and spindle head which were driven by ball-screw and servo motor. While friction force and torque have non-linear position dependence, high repeatability was confirmed. Thus, their non-linearity could be attenuated by identifying friction force and torque beforehand machining operation. From experimental results, it was shown that tooth-pass frequency and second harmonics component of the cutting forces could be estimated accurately by using the CFOB. The results were acquired from control systems of both stage and spindle head.

Abstract: This paper presents a method for the estimation of unknown disturbances for high precision gimbal systems. Alternative to the classical methods of model inversion and filtering, we employ an asymptotically stabilizing controller which achieves the estimation process even in the presence of unstable zeros. The architecture provides an input equivalent disturbance which can be thought to capture all real disturbances in the system as well as virtual ones such as unmodelled dynamics and nonlinearities. The proposed method is illustrated on a 2-axis gimbal system where system identification is followed by the design on an integral linear quadratic regulator as the stabilizing controller which forms the base of the disturbance observer. It is seen that a random unknown disturbance is estimated successfully in the presence of additional gyro noise.

Abstract: This paper addresses a two-degree-of-freedom control system design for positioning de-vices such as table drive systems based on the predictive functional control (PFC). The aim of the paper is to improve the tracking performance of the previously developed disturbance observer-based predictive functional control (DOB-PFC) system. To this end, we derive a transfer function representation of the PFC controller. On the basis of the representation, we apply the zero phase error tracking controller (ZPETC) as a feedforward preview controller. Experiments using a real table drive system are conducted to compare the proposed control system with DOB-PFC. The experimental results show that the tracking error is greatly reduced compared to DOB-PFC.

Abstract: In haptic technology, robot has to contact with objects and human operator. The robot systems must be flexible systems, high accuracy and precision during the operation for safe the human operator. So, analysis of the force response is a necessary ability to design the controller of the robot systems. This paper proposes a methodology to analyze force response by mean of spectrogram analysis. The master-slave robot based on bilateral control is used by human operator. Disturbance Observe (DOB) is used to estimate the force response instead of force sensor to improve the performance of the whole system. Finally, force response is analyzed by spectrogram. The availability of the proposed method is shown in an experiment.

Abstract: Recently, delta robots is widely used in many industrial application because the structure of delta robot is close loop chain and have properties of high rigid body and fast movement. However, the moving part of delta robot is arranged in pattern that influenced by gravity and has an impact on control system. In this paper, we proposed force and position control in master-slave configuration while compensate gravity. The control system using disturbance observer (DOB) to estimate sum of action/reaction force and gravity force of master-slave delta robot instead of the force sensors. The external force on travelling plate of delta robot is estimated by disturbance force on upper and computational gravity force from dynamic model. Moreover, the delta robot may various in size due to the conditioning of workspace, therefore the method to control the task space is proposed. The simulation is conduct to verify the control system, compare the position and force of travelling plate with and without gravity compensation.

Abstract: In this paper, we propose cutting-force-estimation method for a ball-screw-driven system using triple inertia model. In many cases, dual-inertia model is applied to describe the dynamic behavior of the ball-screw-driven system. In this paper, triple-inertia model is applied and cutting force was estimated without additional sensors, such as dynamometer. The cutting force observer is designed, regarding the ball-screw-driven system as two input and three output system. Simulation results indicate that the proposed method enables accurate estimation around the resonance frequencies. Experimental results showed that the proposed method could monitor external force without being interrupted by the inertia forces.Nomenclature

Abstract: The disturbance observer is a specific method of designing a two degree of freedom control structure to achieve insensitivity to modeling error and disturbance rejection. It has been successfully applied in a variety of motion control applications. In motion control, the major sources of uncertainties are friction, inertia, and external disturbances. These uncertainties should be taken into account by any robust motion controller. In this paper, this element is a PD (proportional-derivative) controller. The disturbance observer proves its advantages through the simulation and experiments. With disturbance observer, better tracking performance can be achieved with less control energy.

Abstract: High precise positioning and high-speed performance are demanded for servo mechanical systems in recent industry. However, the nonlinear friction is a main factor to make the positioning mechanism imprecision. To improve the positioning the positioning precision of stages driven by ball-screws, there are two types of compensations including model and non-model based methods. In this study, the LuGre friction Model is applied to model the nonlinear friction behavior for a ball-screw driven stage. A Modified Charge Search System (MCSS) was proposed to identify the system’s parameter. After the system’s parameters are obtained, a feed-forward control integrated with a disturbance observer is proposed to eliminate the external disturbance and improve its tracking performance.