Disturbance observer (DOB) has been one of the most widely used robust control tools since it was proposed by Ohnishi in 1983. This paper introduces the origins of DOB and presents a survey of the ...major results on DOB-based robust control in the last 35 years. Furthermore, it explains DOB's analysis and synthesis techniques for linear and nonlinear systems by using a unified framework. In final section, this paper presents concluding remarks on DOB-based robust control and its engineering applications.
This paper analyzes the robustness and stability of disturbance observer (DOb)-based explicit force control systems. Conventional analysis methods, which only consider ideal robustness, are ...impractical due to the design constraints of a DOb, e.g., bandwidth limitations. This paper shows that not only the stability but also the robustness of a DOb-based explicit force control system changes by environmental impedance variations. The robustness of a DOb-based explicit force control system is clarified by deriving new sensitivity functions. Implicit and explicit environmental impedance estimation methods are considered by analyzing the dynamics of a force sensor and a reaction force observer (RFOb), respectively. It is shown that the stability and performance of an explicit force control system can be improved by using an explicit environmental impedance estimation method, i.e., an RFOb, intrinsically. However, an RFOb is more sensitive than a force sensor to external disturbances, and the stability of the explicit force control system drastically changes by the design parameters of a DOb and an RFOb. Force-sensor- and RFOb-based explicit robust force control systems are compared in terms of stability, robustness, and performance in detail. The validity of the proposals is verified by simulation and experimental results.
Controlling robots in contact with the environment is an important problem in industry applications. Generally, a force sensor is used for sensing the external force. It is well known that ...information of a force sensor has much noise. Furthermore, unstable state is also caused by the narrow bandwidth of force information by a force sensor. This paper shows that stable contact with the environment is difficult when a force sensor is used because of its soft mechanical structure and narrow bandwidth of force sensing. In order to solve the instability of force control, the disturbance observer is implemented instead of the force sensor. The disturbance observer can observe the external force without force sensors. When the disturbance observer is implemented in a robot, a force control system does not include a soft mechanism between a robot and the environment. Since a robot can detect the environmental information directly, a wide bandwidth of force sensing is attained. In this way, this paper solves the problems of force control by considering the force sensing method without changing the control architecture, and the ability of force control is improved. Experimental results show viability of the proposed method
Inclusion bodies are often formed when the foreign protein is over expressed in Escherichia coli. Since proteins in inclusion bodies are inactive, denaturing and refolding of inclusion body proteins ...are necessary to obtain the active form. Instead of the conventional denaturants, urea and guanidine hydrochloride, a strong anionic detergent SDS was used to solubilize C-terminal His-tag form of ulvan lyase in the inclusion bodies. Solution containing SDS-solubilized enzyme were kept on ice to precipitate SDS, followed by SDS-KCl insoluble crystal formation to remove SDS completely. After removing the precipitate by centrifugation, the supernatant was applied to Ni-NTA column to purify His-tagged ulvan lyase. The purified protein showed a dimeric form and ulvan lyase activity, demonstrating that SDS-denatured protein was renatured and recovered enzyme activity. This simple method could be useful for refolding other inclusion body proteins.
•SDS is an effective denaturant of inclusion bodies.•SDS-KCl complex easily removes SDS from the denatured protein.•Renatured ulvan lyase showed the enzyme activity as natural enzyme.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
6.
Motion Control Systems Sabanovic, Asif; Ohnishi, Kouhei
2011, 2011-01-14, 2011-03-10
eBook
Motion Control Systemsis concerned with design methods that support the never-ending requirements for faster and more accurate control of mechanical motion. The book presents material that is ...fundamental, yet at the same time discusses the solution of complex problems in motion control systems. Methods presented in the book are based on the authors' original research results. Mathematical complexities are kept to a required minimum so that practicing engineers as well as students with a limited background in control may use the book. It is unique in presenting know-how accumulated through work on very diverse problems into a comprehensive unified approach suitable for application in high demanding, high-tech products. Major issues covered include motion control ranging from simple trajectory tracking and force control, to topics related to haptics, bilateral control with and without delay in measurement and control channels, as well as control of nonredundant and redundant multibody systems. Provides a consistent unified theoretical framework for motion control designOffers graduated increase in complexity and reinforcement throughout the bookGives detailed explanation of underlying similarities and specifics in motion controlUnified treatment of single degree-of-freedom and multibody systemsExplains the fundamentals through implementation examplesBased on classroom-tested materials and the authors' original research workWritten by the leading researchers in sliding mode control (SMC) and disturbance observer (DOB)Accompanying lecture notes for instructorsSimulink and MATLAB® codes available for readers to downloadMotion Control Systemsis an ideal textbook for a course on motion control or as a reference for post-graduates and researchers in robotics and mechatronics. Researchers and practicing engineers will also find the techniques helpful in designing mechanical motion systems.
This paper presents a force servoing method to suppress torsional vibration of two-mass resonant system. The resonance ratio control is one of the effective control methods of two-mass resonant ...system. In this method, the ratio between the resonant frequency of motor and arm is determined arbitrary according to the feedback of estimated reaction torque. The reaction torque is estimated by using a position sensitive detector (PSD). Since the estimation method does not need the parameter identification, the torsion information is obtained with accuracy. To attain the affinity and adaptability to environment, motion systems should control the reaction torque from the environment. In the force servoing system, the force command is given as a disturbance of the arm portion. The arm disturbance is observed by the arm disturbance observer without force sensors. The proposed force servoing system is based on both the conventional PD control and the resonance ratio control, and the determination method of pole placement is discussed. The proposed force servoing system can realize both the suppression of the inner torsional reaction torque and the adaptation to unknown outer force inputs. The numerical and experimental results show the viability of the proposed method
Time delay in bilateral control system seriously deteriorates performance and stability. Acceleration-based bilateral control (ABC) is hybrid of position and force control in the acceleration ...dimension based on a disturbance observer. It can be divided into two modal spaces: common and differential modal spaces. The sum of master force and slave force is controlled to be zero in common modal space to realize the law of action-reaction. The difference of master position and slave position is controlled to be zero in differential modal space for position tracking. This paper analyzes the stability of each modal space under time delay. Based on modal space analysis, this paper proposes a novel "frequency-domain damping design" using high-pass filter for ABC. The validity of the proposed control system is confirmed by some experimental results.
This paper proposes a new nonlinear stability analysis for the acceleration-based robust position control of robot manipulators by using disturbance observer (DOb). It is shown that if the nominal ...inertia matrix is properly tuned in the design of a DOb, then the position error asymptotically goes to zero in regulation control and is uniformly ultimately bounded in trajectory-tracking control. As the bandwidth of a DOb and the nominal inertia matrix are increased, the bound of error shrinks, i.e., the robust stability and performance of the position control system are improved. However, neither the bandwidth of the DOb nor the nominal inertia matrix can be freely increased due to practical design constraints, e.g., the robust position controller becomes more noise-sensitive when they are increased. The proposed stability analysis provides insights into the dynamic behavior of DOb-based robust motion control systems. It is theoretically and experimentally proved that nondiagonal elements of the nominal inertia matrix are useful in improving the stability and in adjusting the tradeoff between robustness and noise sensitivity. The validity of the proposal is verified by simulation and experimental results.
Biped walking robots have been widely researched because biped walking is considered as an effective way to locomote in human environments. There are a lot of ways to generate biped walking patterns, ...and it is widely known that the model certainty of the robot and the immediate generation of the trajectory are very important. Using preview control is a useful way to generate the walking patterns. By using the preview control method, modeling errors, which are generated by using a simple model, can be compensated by using the preview controller again in the conventional approaches. As a matter of fact, it is known that it takes much time to generate the trajectory by using the preview controller again. In this paper, biped walking pattern generation by using preview control based on a three-mass model is proposed. By using the proposed method, the modeling errors can be decreased without using the preview controller again, which means that the immediate generation of the trajectory can be achieved. The validity of the proposed method is confirmed by numerical examples and experimental results.
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