This paper focuses on voltage-integral-based reference tracking modulation (VIRTM) and direct torque control (DTC), proposing the control strategy that minimizes switching frequency while achieving excellent dynamic performance. In the proposed scheme, the optimal voltage integral trajectory calculated by exhaustively searching all switching patterns in an offline process is applied to the DTC. One of the advantages of the proposed scheme is its superior versatility and robustness, as it does not rely on motor parameters. Secondly, it significantly reduces the switching frequency at all operating points while preserving the dynamic characteristics of DTC. The effectiveness of the proposed scheme has been validated through experiments, demonstrating up to a 28% reduction in switching frequency compared to conventional standard DTC.

This paper presents a modulation method that minimizes the impact on common-mode noise and switching loss. The proposed method introduces a priority factor into the evaluation function to satisfy both requirements and adjust these characteristics. The effectiveness of the proposed method is tested through simulations and experiments, which confirm the switching and common-mode voltage frequencies.

Advancements in automation have pushed forward the development of collaborative robots, which are designed to work together with humans. The majority of actual commercial collaborative robots use geared motors with some kind of torque sensing, and their performance is directly related to how well torque is controlled. However, imperfections in the gear fabrication causes transmission error in the geared motor, producing undesired vibrations which affect the torque control performance. In this study, an integratorless 2DOF (two degrees-of-freedom) torque control scheme is proposed to improve the torque response in such case. The proposed control scheme uses first-order FPIDO (force-position-integrated disturbance observer) which nominalizes and achieves motor side acceleration control, allowing to use the natural mechanical dynamics of the motor side as an integrator instead of implementing it on the control system. This is combined with a derivative-type torsional disturbance observer (DTDOb), which uses torque sensor information to compensate all torsional disturbances and nominalize the torsion torque dynamics, achieving 2DOF (Two degrees of freedom) torque control. The effectiveness of the proposed methodology is verified by simulation and experimental results.

This paper proposes a load-side acceleration control scheme for geared motors affected by unknown backlash and friction. A backlash-deactivated disturbance observer (BDDOb) is proposed to achieve load-side acceleration control while ensuring quick traversing of backlash. The BDDOb works by executing conditional estimation-compensation of load disturbances, and is driven by a backlash detection scheme based on torsion torque sensing which does not require any information on the backlash gap width. In addition, a variable-order force-position-integrated disturbance observer (VOFPIDO) is proposed to quickly compensate nonlinear friction without requiring information of the nonlinear friction magnitude by applying velocity-dependent switching. Experimental results prove the effectiveness of the proposed method.

This paper focuses on single inertialization on the load-side parameter of two-inertia system and employs the equivalent disturbance compensator (EDC). Conventional EDC is designed in case of the plant system without friction; thus, the back-forward drivability control using the EDC is affected by friction. In this paper, we propose the back-forward drivability control using EDC and DOB for single inertialization of two-inertia system. DOB is used to compensate the friction and the EDC is applied to not only improve the back-forward drivability, but also suppress the vibration on load-side output. This proposal consists of basic actuator and force sensor and it is available to general robot actuator that uses current sensor, motor encoder, and force sensor. The effectiveness of proposed back-forward drivability control is verified through the numerical simulation.

Good forward-drivability characteristics are essential for applications such as position, velocity, and force control. Geared motors, usually employed in industrial robots, require lubrication in their gears, and consequently, some form of sealing is needed to avoid leaking. While oil seals prevent leaking, they increase nonlinear frictional effects, which result in stick-slip during velocity zero-crossings, thereby deteriorating the forward-drivability. This paper proposes a stick-slip suppression method based on a velocity-driven N-order stick compensator (VDNSC), which works as an order-variable friction compensator formed by the velocity-driven switching of the internal components of a high order Q-filter. Experiments with torque and velocity control confirm that the proposed method improves the forward-drivability, allowing for more precise motion even under large friction.

This paper proposes a new sensorless force sensing approach to realize the advanced wideband force control system. The force observation is based on the harmonic estimation integrated singular spectrum analysis based disturbance observer. The singular spectrum analysis is constructed to improve the force sensing performance and achieve the remarkably wide bandwidth by effectively separating the fundamental response and noise when the disturbance observer pole is notably raised. Additionally, the harmonic estimation based on the least squares method is configured to identify and cancel the periodic component caused by dither signal in the force estimation. The proposed method achieves the high performance force sensation with considerably widened force sensing bandwidth. The effectiveness of the proposed method is verified by numerical simulation results.

Load-side acceleration sensing based on load-side acceleration control is proposed for a two-inertia resonance system. The proposed method is divided into two stages. In the first stage, the feedback component from the load-side is canceled using the estimated value of the instantaneous state observer and the load-side acceleration. The two-inertia resonance system is converted into a simple second-order system using this method. The proposed method configures a control system of cascaded loops for the second-order system. Therefore, the load-side acceleration control is achieved by two specified bandwidths. The proposed method is easy to implement for conventional robots and yields superior cost-savings compared with other types of load-side acceleration control. The effectiveness of the proposed load-side acceleration controller is verified by theoretical analysis, numerical simulations, and experiments.

In a single-phase to three-phase electrolytic capacitor-less inverter, the inverter must control not only the motor but also the source current because a power factor correction circuit or energy buffer does not exist. To obtain a sinusoidal source current, a control method that modifies the output voltage directly is proposed. However, the motor current control occasionally becomes unstable because the control method modifies the output voltage to control the source current. To control the source current while considering the motor current response, this paper proposes a motor current regulation based direct DC-link current control. The proposed method enhances the stability of the motor current control system by realizing the sinusoidal source current with the motor current reference modification. The effectiveness of the proposed method is experimentally verified.

In this paper, we develop a wireless power transfer (WPT) system using a virtual-current source resonant inverter (VCSRI). The concept, theoretical analysis, simulations and experimental results have been reported. With the current source feature, there have been various advances such as the sort-circuit protection and the reduction of current stress on switching devices. To validate the proposed WPT system, a scaled-down laboratory hardware prototype was built and tested. Then, the results were revealed that the proposed WPT could work properly when compare between simulations and experimental results. The comparison of maximum dc to dc power efficiencies between the conventional system (without control) and the proposed system (VCSRI) were 52 % and 60 %, respectively.

In the electrolytic capacitorless inverter system, resonance occurs between the inductance on the grid side and the DC-link capacitor. Because of this resonance, the regulation of the input current harmonic may not be satisfied in some cases. In order to satisfy harmonic regulation, a method for controlling this input current by direct DC-link current control has been proposed using PWM modulation. In PWM modulation, the switching frequency depends on the carrier frequency. This paper proposes a control method that reduces the switching frequency and satisfies the harmonic regulation via model predictive direct current control (MPDCC). This paper is confirmed that the proposed method reduces harmonics of input current and switching frequency. The effectiveness of the proposed method is verified by numerical simulation.

In this paper, we present a method to rapidly discretize a continuous time-variant system in real time. Three discretization methods are compared. The proposed method does not calculate for discretization, and therefore, the calculation cost is 1/100 of that of the conventional zero-order hold model. The presented method has high stability in higher order systems and the position and size of the internal parameters are determined for each sampling time. The effectiveness of the Finite-Difference Time-Domain (FDTD) method is demonstrated by comparing responses with a continuous system by using simulations. By experiments, we reproduce the haptic sensations based on the time-variant environmental model expressed by Tustin approximation and FDTD method.

In order to realize a fine force sensorless force control, this paper proposes a new notch-type friction-free disturbance observer(DOB) and a new notch-type friction-free reaction force observer(FFRFO). Generally, a force sensorless force control system always has influence on static friction phenomenon. To overcome this problem, this paper proposes a new force sensorless control system using the notch-type friction free reaction force observer, whose inner system is the proposed acceleration control based on the notch-type friction free disturbance observer. The effectiveness of the proposed system is confirmed by experiments using an actual industrial robot.

In a single-phase to three-phase inverter that does not have an inductor or electrolytic capacitor, the inverter must control not only the motor but also the input power factor because there is no power factor correction circuit or energy buffer. To improve the input power factor, several control methods are proposed. However, if the motor has large spatial harmonics caused by the rotor structure, the bandwidth limitations of the control system adversely affect the source current response and thereby cause source current harmonics. This paper proposes a harmonic current reduction controller that makes it possible to obtain a sinusoidal source current. The proposed controller focuses on the relationship between the source current and the average DC-link current and controls the source current using a feedforward control method. The effectiveness of the proposed method is experimentally verified.

This paper proposes a robust position control based on state feedback using double disturbance observer for two mass system. In load-side position control based on state feedback using disturbance observer, performance of control system is depend on bandwidth of disturbance observer. To solve problem, the load-side position control using I2-PI controller based on state feedback is proposed. The proposed system consists of PD position controller, motor-side acceleration controller, I2- PI controller equivalent of states feedback, velocity deviation feedback, and a zero-order load-side disturbance observer (ZLDOB) with variable noise-covariance (VNC) Kalman filter. The simulation and experimental results confirm that the load-side position control using I2-PI controller based on state feedback reduces the vibration in response load-side position. Additionally, the proposed method reduces the vibration in response load-side acceleration.

For the high performance of force/torque control, an approach using a disturbance observer is known to be effective. However, a conventional disturbance observer cannot perfectly compensate for the disturbance torque when the disturbance torque (for example, impact torque) is instantaneous. This paper proposes a force and position sensors integrated disturbance observer (FPIDO), and analyzes its disturbance-suppression performance. Moreover, this paper focuses on high-performance torque control using a torsion torque sensor for a two-inertia system. The disturbance-suppression performance of the conventional disturbance observer and the FPIDO are compared using experimental results for motor-side acceleration control and load-side torque control. Finally, the experimental results verify the effectiveness of the proposed disturbance observer.

Human-robot collaboration systems have attracted more and more researchers' attention. Many experiments in a new design of robot system illustrated that it can be used to help and support human operator. In the past few decades, delta robots have popular usage in industrial applications, especially in picking and packaging for their relative advantages such as high speed, high accuracy, and light weight devices. Delta robot is a parallel manipulator that consists of three arms connected to universal joints at the base. This paper presents work on a new force sensor less haptic human-robot collaboration system based on 3D parallel mechanism delta robot. The controller of delta robot was designed by using force sensorless bilateral control approach with considering of gravity compensation. Each joint of the AC servo motor can be programmed to estimate the external force from unknown environment by using the disuturbance observer (DOB). It was shown that delta robot can not only be applied for industrial applications, it can also be conveniently used for human-robot interaction. Experimental results are presented which demonstrate that the gravity effect can be compensated. Therefore, our proposed robot system is suitable for human-robot collaboration system.

This paper proposes a new sensorless force control system based on reaction force estimation system considering static friction and kinetic friction for industrial robot. As industrial robot uses the harmonic gear and the ball screw, the proposed force control system is structured by the resonance ratio control based speed controller. Moreover, as harmonic gear has a static friction and kinetic friction, the reaction force estimation system needs to reduce the influence on static friction and kinetic friction force. The proposed friction-free force estimation system has the two technics. The first one is the dither signal based static friction free force estimation, and the second one is the Stribeck model based kinetic friction free estimation. Using these technics, the friction-free reaction force estimation system is constructed. In this paper, the validity of proposed system is verified by the experimental results using the actual industrial robot.

This paper proposes a current harmonics control method for the input current of an electrolytic capacitor-less inverter for an interior permanent magnet synchronous motor (IPMSM). In general, an IPMSM has large spatial harmonics caused by the rotor structure. The back electromotive force (EMF) of an IPMSM contains harmonics and generates three-phase current harmonics. The three-phase current harmonics result in the input current harmonics of an electrolytic capacitor-less inverter because the power converter system has little energy storage on the DC-link. This paper analyzes an input current harmonics generation mechanism based on averaged DC-link current. The proposed control method that controls the input current harmonics is based on the analysis mechanism. The validity of the proposed method is confirmed through simulation and experimental results.

This paper focuses on storage and reproduction systems for environmental haptic sensations. A large force vibration is caused by the differential of viscosity momentum in the reproduction system based on force control. To solve this problem, the reproduction system based on momentum control has been proposed in previous our research. The improved reproduction system has a configuration that the momentum control loop is added to the force control loop. The high-stiffness environment in which the actuator does not move cannot be reproduced because the system generates the force command that correspond to the position of the actuator. Hence, this paper newly proposes storage and reproduction systems based on position control considering the environmental mechanical admittance. The proposed system is able to reproduce the environmental information without additional control loop. The effectiveness of the proposed method is confirmed by experiments.

This paper proposes a frequency separation type current control system for a grid-connected single-phase five-level inverter. The proposed control system realizes high tracking performance and high disturbance suppression performance. To obtain high tracking performance to the sinusoidal reference signal, a repetitive controller is applied to the current controller. The current controller with a repetitive controller is capable of tracking to fundamental frequency, without the steady-state error. The disturbance observer using a notch filter (notch type disturbance observer) is used to obtain the high disturbance suppression performance. Using the notch type disturbance observer, the frequency components except for the fundamental frequency are suppressed. The proposed control system is configured by combining the current controller with a repetitive controller and a PI controller, and adding a notch type disturbance observer. Numerical simulation results and experimental results confirm that the proposed control system effectively reduces the output current distortion. The THD of the output current is reduced by 15.5 % when using the proposed control system.

In the recent times, the number of amateur farmers has been increasing. Although amateur farmers use tillers, they may find it difficult to drive the tiller along a straight line. There is a need for electric tillers with independent drive wheels. This paper proposes straight control incorporating human driving input by using a disturbance observer. Numerical simulation results and experimental results confirm the validity of the proposed method.

Recently, a soft robot considering the contact of the human has attracted attention, and the zero stiffness torque control is required. Because a soft robot causes vibration at the load side, vibration suppression control of a soft robot is required. In this paper, the authors discuss position control and torque control of a soft robot by using a torsion torque sensor based on a resonance ratio control. Position control can be used to design parameters. However, torque control cannot be used to design parameters because the proportional gain Kp and resonance ratio gain Kr are not independent with regard to integral-proportional differential(I-PD) torque control. Therefore, in the case of torque control, resonance ratio control is equivalent to I-PD control.

This paper proposes a current compensation method for current reconstruction from a DC-link current sensor. The method has region in which phase current reconstruction is difficult. To solve this problem, voltage reference and carrier compensation methods have been proposed. However, these methods increase the phase current harmonics. This paper proposes a current compensation method that uses the phase difference between the current and the voltage reference. The effectiveness of the proposed method and characteristics of reconstruction current feedback control are confirmed using a simulation. Experimental results verify the validity of the proposed current reconstruction method.

Recently, the human-robot interaction systems are extending their capability to work in many applications. Appropriate haptic devices or robot systems have an important role to support the collaboration task which require close interaction between human and robot. This paper proposes a novel 3D parallel mechanism delta robot based on Kalman filter based state observer for the haptic devices. In the mechanical design, a 3D parallel mechanism delta robot contains three identical and symmetrical upper-arm and fore-arm of parallel links that are connected to the base plate with motor at lower end and to the end-effector with a ball joint at top end. The delta robot are designed and analyzed in order to realize a 3D motion in the workspace of the robot's end-effector. In the controller design, Kalman filter based state observer, (KFSO) can be applied to estimate an external torque of motor. With such a force sensorless control scheme based on the feedforward disturbance torque compensation loop, significant high bandwidth haptic sensing in a delta robot system can be achieved. The proposed method has been successfully applied in a real delta robot system in order to show its applicability. The experimental results of the rehabilitation robot are provided to illustrate the performance of the proposed algorithms. In the experimental results, the system was able to estimate a 3D motion and external force in the workspace of the robot's end-effector.

In the field of high-precision position control, the position response requires that there is no vibration. However, a permanent magnet synchronous motor (PMSM) has a wide variety of torque-ripple components, including cogging torque and flux harmonics, which degrade the control performance. Typically, these components are defined as a disturbance torque, and compensation is accomplished by using a disturbance observer. However, a disturbance observer uses a low-pass filter for noise reduction, and it causes phase and amplitude shifts in an estimated value. As a result, it is not possible to perform the appropriate compensation. This paper considers a new structure of disturbance observer based on a zero-order disturbance observer and torque ripple table. It is possible to accurately estimate the instantaneous disturbance torque by using the proposed disturbance observer. The effectiveness of the proposed disturbance observer is confirmed by numerical and experimental results.

This paper proposes a sensorless vector control method based on Primary flux linkage and sinusoidal current tracking control for Interior permanent magnet synchronous motor. The proposed sensorless vector control can control torque at different speeds. Furthermore, the proposed sensorless vector control method estimates the primary flux linkage vector. At various speeds, it is possible to control the torque without relying on position or speed information.

This paper proposes a transmission torque linearization method for a leg robot using bi-articular simultaneous drive mechanism. A planetary gear is the primary mechanism of a bi-articular simultaneous drive system. Energy consumed for walking is reduced by the use of bi-articular muscles. However, the planetary gear causes a torque transmission loss in the leg robot system. The proposed method linearizes the nonlinear torque transmission by using a disturbance observer and the estimated self-weight disturbance torque. The experimental results point out that the proposed method linearizes the transmission torque.

This paper proposes a stable force control system to achieve the force control of industrial robots. The proposed stable force control system is designed by using an I-P force control system and a resonance ratio control system considering the required interaction with the environment. To design the resonance ratio control system considering the contact with the environment, this paper analyzes the stability of the proposed resonance ratio control and the bandwidth of a disturbance observer. This paper designs the resonance ratio control system using an instantaneous state observer considering the results of the stability analysis. In addition, a stable force control system is designed based on the resonance ratio control system using an instantaneous state observer. In this paper, the effectiveness of the proposed force control system is confirmed by performing numerical simulations and experiments using an industrial robot arm.

The approach used to implement mechanical impedance can be generally separated into the following two types: an impedance control system and an admittance control system. When an impedance control system reproduces a hard environment, large vibrations are generated. In contrast, an admittance control system is excellent at reproducing a high-stiffness environment for utilizing the inverse of the environmental impedance. However, stability analyses have not been conducted on admittance control systems. Therefore, in this study, a stability analysis for an implementation system of mechanical impedance is conducted using a pole placement. The analysis results indicate that the pole placement of the impedance control system is moved toward the direction of an imaginary axis based on the influence of the environmental stiffness. Hence, large vibrations occur when the environmental stiffness is determined to be a large value. On the other hand, for the admittance control, when the environmental stiffness is dominant, pole placement is not affected by the environmental stiffness. The superiority of the admittance control system in a high-stiffness environment was shown through an experiment.

This paper proposes a control method to realize interior permanent magnet synchronous motor (IPMSM) drive system without using both an electrolytic capacitor and an line inductor. In general, an electrolytic capacitor-less inverter shows input current vibration in the source side if there is a line impedance on the source. This vibration is caused by resonance with the line impedance and the DC-link capacitor. The current vibration causes current distortion and lowers the power factor. In general, the input current vibration has high frequency components because of low line impedance values. Thus, in order to reduce the input current vibration using the conventional dumping feedback control, it is necessary to lower the frequency by adding an inductor to the line impedance. In this paper, the authors propose a method that adds a cancellation voltage pulse to the three-phase voltage reference of the inverter, in order to prevent input current vibration. The simulation and experimental results confirm that the proposed method reduces the input current vibration effectively. The maximum power factor obtained by using the proposed method is 98.09 % and THD is 17.95 %.

This paper proposes a new wideband bilateral motion-scaling control to apply in the small size robot system. The scaling Hadamard matrix is applied to reduce or magnify the force and position response of bilateral motion-scaling control. The technique to estimate the action/reaction forces of master-slave robot is designed using Kalman-filter based disturbance observer (KFDOB). Optical encoder and acceleration signals were fused to estimate contact forces occurring during an experiment. With the bilateral motion-scaling control and KFDOB, we can control the small scale master-slave robot with high precision. Comparative experiments show the KFDOB and its multi-sensor fusion to provide performance superior to that of previously disturbance observer. As seen in the experimental results, it is clear that high transparency and good perception of the environmental stiffness with the response of the master-slave robot can be achieve successfully. An additional result of FFT analysis which guarantees noise compensation is also presented.

This paper describes a control method for the self-sustained operation of a photovoltaic (PV) generation system to compensate the output voltage distortion compensation. In order to improve the output voltage distortion, the control circuit consists of sinusoidal tracking control based on the internal model principle. Moreover, the control system is configured by combining the sinusoidal tracking control and a notch type disturbance observer. Thus, this configuration of the control system produces lower output voltage distortion. In addition, the zero location of sensitivity function is relocated by appropriately modifying the feedback element of the disturbance observer. The simulation and experimental results confirm that the proposed disturbance observer effectively reduces the output voltage distortion and improves the disturbance suppression characteristics. The THD of the output voltage is improved by 3.15 % using the proposed zero re-allocated disturbance observer in the case of the resistance and rectifier.

This paper proposes a method of dynamic parameter tuning for a sensorless force control system with I-P(Integral-Proportional) current controllers. All free parameters of the whole system are determined theoretically by pole assignment method. This paper describes that gain of current controllers and estimation bandwidth of a disturbance observer have to be set according to stiffness of target environment, although gain of a force deviation and a quality factor of the disturbance observer are derived as constant values. In order to adapt to the stiffness variation, the proposed system changes dynamically the gain of I-P current controllers and the bandwidth of the disturbance observer. Furthermore, comparative experiments confirm that the force and I-P current control systems with dynamic parameter tuning is effective.

This paper describes a soft-switching-interleaved power factor correction (PFC) converter. The proposed PFC converter reduces the input-current ripple by using an interleave-control method and realizes high efficiency through the soft-switching operation of all switching devices, without requiring a large auxiliary resonant circuit. In order to confirm that the proposed converter achieves soft-switching operation, a prototype of the PFC converter was experimentally investigated. The experimental results indicate that the proposed converter can realize soft-switching operation on all switching devices, reduce the amount of input current ripple, generate a unity input power factor of 99% or more, and maintain both a sinusoidal input current and a constant output-voltage control. The efficiency of the proposed PFC converter with a lossless snubber is higher than that of the PFC converter without the snubber. Moreover, an improvement technique for reducing the power-source current distortion is proposed. Improvement in the amount of source-current distortion is confirmed by using a waveform-improvement method in both the simulation and the experiment, reducing the total harmonic distortion (THD) by 2.74%.

Papers dealing with sensors or actuators published in IEEE Transactions on Industrial Electronics (TIE) and IEEE Transactions on Industrial Informatics (TII) during the year of 2011-2013 have been surveyed in this paper. The papers are roughly categorized according to their subjects.

This paper proposes a current harmonic reduction method to improve the input current waveform in electrolytic capacitor-less single-phase to three-phase power converters. Typically, the back EMF of an IPM motor is not sinusoidal and contains harmonics caused by the rotor structure; therefore, it causes harmonic distortion in the motor control system and generates harmonics in the input current. In this study, the cause of the input current harmonics induced in the back EMF and the d-q axis current controller are analyzed. Furthermore, this paper proposes a control method to reduce the current harmonic distortion. In the proposed method, the d-q axis voltage references are compensated to reduce the input current harmonics. The d-q axis compensation voltages are obtained by a feed-forward controller. The maximum power factor obtained by the proposed method is 98.0[%]. The experimental results confirm that the proposed control method conforms to the EN61000-3-2 guideline.

The force control system of a typical injection molding machine obtains force information from the machine's environment via a force sensor. However, because of Force sensors often have disadvantages such as signal noise, high cost, and a narrow bandwidth, a reaction force observer was developed for electric injection molding machines. This method has a steady-state error owing to the influence of nonlinear friction. We realized sensorless force feedback control based on a friction compensation element, dither signal inserting method, and high order reaction force observer (HORFO). The HORFO does not influence either the inserted dither signal or the nonlinear friction phenomenon. However, as the desired parameters of the HORFO cannot be fixed at each driving point, the sensorless force feedback control method cannot always be used for fine pressure control. To overcome this problem, we propose new sensorless force control system based on HORFO in this paper. Experimental results confirmed the robustness of the proposed sensorless force control system.

Pickup systems for optical disks operate in the horizontal and vertical directions for tracking and focusing, respectively. Conventional optical disk control systems are designed for each operated direction. On the other hand, in this paper, we consider the operation trajectory to implement a method for concurrent control of focusing and tracking of optical disks. This paper proposes a two-dimensional feedforward control system. The proposed control system consists of a feedforward controller and a two-dimensional feedforward compensator. The error vector is a combination of the focusing error and the tracking error of the compensator. The feedforward controller based on a zero phase error tracking control (ZPETC) regulates the error vector. The experimental results show the effectiveness of the proposed control system.

Force sensing is an important part of a motion-copying system. To achieve the high performance of the control system, high quality of force sensing is required. This paper focuses on suppressing harmonic disturbances in the force estimation to improve the performance of force sensing. A friction-free disturbance observer with a dither signal is applied for both motion-saving and motion-loading systems. The dither signal reduces the friction effect on force estimation and the friction-free disturbance observer eliminates the oscillatory signal on force estimation. Moreover, the friction-free disturbance observer achieves effective harmonics suppression in force estimation. All control algorithms are implemented in FPGA to achieve short sampling period, and enable a wider force sensing bandwidth. The effectiveness of the proposed method is verified by experimental results.

Generally, the flexible robot system can be modeled as the two-mass system which consists of a motor and load connected by a spring coefficient. In order to achieve accurate tracking objectives, the correct of parameter identification in the model based controller is necessary. The objective of this paper is the parameter identification of a spring coefficient of flexible robot system. The multi-encoder based disturbance observer (MEDOB) and load side disturbance observer (LDOB) are employed to identify a correct spring coefficient parameter of flexible robot system. The comparison of external force estimation between MEDOB and LDOB is used to find the correct value of spring coefficient. By using the proposed identification method, it is simple to identify the spring coefficient and easy to implement in the real flexible robot system. The effectiveness of the proposed identification method is verified by simulation and experimental results.

AC servo motors are operated by current sensors. However, these current sensors often exhibit offsets caused by age-related deterioration and thermal variation. Gain deviation also causes current measurement errors. These errors lead to torque ripples and dq-axis current ripples. This paper proposes a new method of estimating and compensating for gain deviation in current measurement using a current simulator. The method uses dq-axis current ripples arising from sensed current and estimated current. Thus, it can be applied in conjunction with a proposed offset estimation method. In this paper, the methods are tested on a surface-mounted permanent magnet synchronous motor, in which the current sensors are arranged in u-phase and w-phase. Simulation and experimental results confirm that the proposed methods suppress current and torque ripples caused by offset and gain deviation in current sensors.

This paper presents a new method to obtain high resolution position using the incremental encoder signal. In addition, the high resolution position has been used for velocity estimation and torque disturbance estimation by disturbance observer. FPGA implementation is performed using short sampling time, which offers high performance in the motion control algorithms. The high position estimation is produced by the normalization of the number of clock pulses per pulse encoder. Thus, the fractional step can be evaluated at every sampling time. So, the fractional step is integrated every sampling time to the incremental encoder signal. The position with high resolution reduces the noise in the velocity estimation and torque estimation; thus, their bandwidth can be increased. The proposed method is verified in a velocity control and force control based on disturbance observer.

In this work, we present a bilateral control system with different mechanisms of master and slave sides. A linear shaft motor and a ball screw perform the roles of the master and slave, respectively. To reduce the friction effect on force estimation due to the ball screw mechanism, a periodic signal is inserted into the control signal of the slave side. The addition of periodic signal causes oscillatory force responses on both master and slave sides. Therefore, a high-order disturbance observer is designed for force sensing operation on the slave side to reduce the effect of oscillatory disturbance on force information. The control algorithm consists of a conventional disturbance observer and a high-order disturbance observer for master and slave sides, respectively. The numerical simulation results verify the effectiveness of the proposed method.

Trains require high deceleration and stable traveling performance. The improvement of adhesion characteristics is, thus, very important for electric trains. Previously, we have proposed an anti-slip/skid re-adhesion control system based on a disturbance observer, with a high adhesion force utilization ratio. In the present work, we focus on the deceleration mode. Generally, a train has an electric regenerative brake (electric brake) and a mechanical brake (air brake). Under wet railway track conditions, the regenerative brake may fall into abeyance caused by the mechanical brake response. This paper considers a blended braking control and proposes a regenerative brake priority control. This paper evaluates and discusses regenerative brake priority control using numerical simulations.

This paper proposes a new control method to reduce the input current harmonics of electrolytic capacitor less single-phase to three-phase power converters. Typically, the back EMF on IPM motor is not sinusoidal and contains harmonics caused by the rotor structure; therefore, it causes harmonic distortion in the motor control system and generates harmonics in the input current. In order to improve the input current waveform, this paper proposes a multi-loop repetitive control method in q-axis current. Furthermore, this paper proposes a d-axis current control method, which reference is made in synchronous with the source voltage. The experimental results confirm that our proposed method effectively reduces the input power current harmonics. THD of the proposed method obtains 17.6[%]. The maximum power factor of the proposed method obtains 98.5 [%].

This paper studies motion reproducibility of a motion-copying system, which is capable of storing and reproducing motion of human operators. In the paper, the motion reproducibility is expressed as transfer function from a force response of the storage phase to a force response of the reproduction phase. According to analysis of the derived transfer function, this paper confirms that the motion reproducibility is varied depending on variations of force gain, position gain, bandwidth of disturbance observer, environmental stiffness, and viscosity frictions. By the experiment, validity of the analysis method of the motion reproducibility is verified.

This paper proposes a new acceleration control method for industrial robots. To achieve high-speed and high-precision path tracking control, the motion control system must be able to control the arm acceleration. However, it is difficult to directly control the arm acceleration, because the speed reduction mechanism of industrial robots has axial torsion. To solve this problem, this paper proposes a new acceleration control method based on an inverse system. The proposed method designs an inverse transfer function system from the current command for arm acceleration. Acceleration control is achieved by the feed-forward control input designed from the inverse system. In addition, a robust feedback control system is designed to compensate for the dynamic disturbance torque and parameter variation. The effectiveness of the proposed method is confirmed by experimental results using a 2-DOF robot manipulator.

The authors propose the force control of a robot manipulator without a force sensor. The proposed force control system is realized by both the acceleration controller and the force observer. Both systems are designed by the mixed-sensitivity H/sup infinity / design method. The acceleration controller regulates the actuator of the robot manipulator by the acceleration control command. The force observer estimates the reaction force from the target environment. The experimental results showed that the response of the proposed force control system without a force sensor coincided with that of the force control system with a force sensor.>

A decentralized manipulator joint control is proposed, based on the model-following acceleration control system which is constructed using only the information from a rotary encoder. When each joint of the robot manipulator is regulated by the proposed acceleration control system, it is not affected by its dynamical nonlinearity and is controlled independently. A continuous-path tracking method for fast-motion control is also designed using the acceleration control. Experimental and numerical examples show that the proposed acceleration control method is valid for multi-degree-of-freedom robot manipulators.>