The thrust of an axial-flow impeller may oscillate at high speeds, owing to disturbances in the thrust direction and the natural oscillation of the propeller. Therefore, in this paper an angular velocity controller equipped with a reference governor is designed based on the critical velocity identified using an elastic body model of the propeller. The objective is to control the angular velocity of the impeller while reducing impeller oscillation in the critical velocity range. The proposed algorithm suppresses impeller oscillation in the thrust direction by avoiding operation the near the critical velocity. The experiments conducted in this study validate the proposed method.

In this study, a position controller and an acceleration controller for an articulated robot are designed. The active joints of the robot are equipped with low-rigidity couplings to realize contact force control. The shaft torsional torque of these couplings is estimated using encoders installed on both the input and output shafts. This estimated torque is utilized to achieve target tracking and disturbance suppression. Herein, we compare three methods for utilizing the shaft torsional torque: the first method does not employ shaft torsional torque feedback (Comparison Method 1), second method applies a constant multiplier to the shaft torsional torque before feeding it back (Comparison Method 2), and third method feeds back frequency-shaped shaft torsional torque (Proposed Method). The simulation and experimental results validate the effectiveness of the proposed method.

The purpose of this paper is to design a load-side angle control system for an electromagnetic motor with a motor/load-side encoder, reduction gear, and low-stiffness coupling. A method of estimating and feeding back the shaft torsional torque has been proposed to suppress shaft torsional vibration at high speed operation. However, feedback of the shaft torsional torque degrades the disturbance suppression characteristics in the low-frequency range and may cause errors in the load-side angle response to the load-side angle command. The authors have proposed a method to improve the disturbance suppression characteristics by suppressing the feedback amount of the low-frequency component of the torsional torque. The effectiveness of the proposed load-side angle control system under varying load-side inertia is confirmed by simulation and experiment.

The relationship between the ankle joint angle and the ankle joint torque during passive motion can be represented by a model using a time-varying elastic modulus. However, the current method assumes the viscosity term to be zero, resulting in modeling errors when the ankle joint is in passive motion at high angular velocities. To address this issue, this study adds a viscous term to the model. The validity of the proposed model is confirmed by the close match between the elastic torque obtained by subtracting the estimated viscous torque from the viscoelastic torque under experimental conditions with varying angular velocities.

In the super-aged population, an assistive device for walking is important for rehabilitating and maintaining elderly people's lower limb muscle strengths. Meanwhile, the assistive device should be lightweight and able to assist the multiple joints. Therefore, the purpose of this study is to develop a tendon-driven assistive device that can assist multiple joints with a single actuator. This paper mathematically derived the dynamics of the device. Besides, by using “Opensim”, it determined the assisting period to tune or decrease the muscle exertion. From two experiments regarding to the statics and dynamics, it validated the mathematical model. By comparing the numerical simulations with the experiments, it could confirm the assistive torque and joint angles of the device were almost equal in the steady state between the simulation and experiments.

In order to reduce the weight of industrial and collaborative robots and also improve force control performance, the tip of the motor output shaft and reducer output shaft may be configured with low-rigidity mechanical parts. The problem with this, however, is that the mechanical resonance frequency decreases, and, as a result, vibration is more likely to occur during high-speed operation. To solve this problem, a method of suppressing vibration by feeding back the torsional torque of the low-rigidity mechanical parts, but this leads to excitation of vibration and steady deviation due to estimation error occur. Therefore, in this paper, we propose a torsional torque estimator with a backlash model that uses both motor angle and load angle through low-rigidity machine parts. The effectiveness of the proposed method is illustrated through simulations and experiment.

In this paper, the position of a two-degree-of-freedom parallel robot with rotary motors is controlled. A low stiffness coupling is inserted between a motor output shaft and a link. The angle of the motor output shaft (motor-side angle) and the angle of the output shaft of the low-stiffness coupling (load-side angle) can be measured by encoders. A disturbance observer is utilized for disturbance compensation. A comparison is made between the case without shaft torsion torque feedback (the conventional method) and the case with shaft torsion torque feedback (the proposed method). The validity of the proposed method is verified using a simulation and experiment.

Bilateral control systems including propeller-driven systems have been researched for tasks such as swiping motion, cooperative grasping and manipulation. Although some studies have proposed static controllers that do not change the gain of the controller, they are not robust against a modeling error in the stiffness of a contact object. This paper proposes an adaptive controller that estimates the stiffness of a contact object in real time and uses the stiffness for a control gain. The validity of the proposed controller is verified via simulations and experiments.

The control performance of a propeller propulsion system depends on its rotor thrust control performance. When a rotor thrust controller that includes a constant-thrust-coefficient model is utilized, rotor thrust response sometimes does not track rotor thrust command. This paper, therefore, proposes a novel rotor thrust controller whose thrust coefficient is a function of airspeed and rotor angular velocity. The validity of the proposed controller is verified by simulation and experiment.

Actuators that have characteristics such as light weight and high torque-to-weight ratio and good torque control performance are desirable for finger robots and power-assist suits. Although electromagnetic motors excel in torque control performance, they have low torque-to-weight ratios, and although electromagnetic motors with reduction gears have high torque-to-weight ratios, backlash and friction degrade torque control performance. This paper therefore proposes a load torque control system using an electromagnetic motor with motor/load-side encoders. The validity of the proposed control system is verified via simulation and experiment.

Contact-force control of aircraft involves aerial tasks that require making contact with other objects. Conventional contact-force controllers for propeller-driven systems utilize a contact-force feedback controller. Although the controller gain must be increased to improve performance, it is difficult to increase because of stability constraints. This paper therefore proposes a novel contact-force controller that includes two state feedback controllers in addition to a contact-force feedback controller. The estimated thrust-force and the estimated velocity of a body are fed back to the contact-force controller. The validity of the proposed controller is verified through simulation and experiment.

In the case of compressors, frame vibrations cause significant noise problems. In former research, several solutions are presented based on additional sensors, such as accelerometers. However, since the use of sensors includes negative aspects such as high cost and more space, the research on additional sensorless skill is a hot point. In this paper, a novel sensorless anti-vibration system for PMSM-drive applications called Specific Component Reduction System (SCRS) is proposed. This system uses a novel controller called SCRC instead of repetitive controller. The stability of SCRS is analyzed. Experimental results show the effectiveness of the proposed system.

Communication delay between a master robot and a slave robot destabilizes a bilateral control system. A few recent research studies have shown that an adaptive controller that dynamically determines the gain of master controller depending on the stiffness of a contact object is effective in improving stability. However, since conventional adaptive controllers are designed in a joint space, the controllers do not work when the structure of a master robot is different from that of a slave robot. Thus, this paper designs an adaptive controller in a workspace. The validity of the controller is verified via an experiment of a bilateral control using a two degree of freedom manipulator.

This paper proposes a force control system for a single-rotor helicopter. The rotor blade's lift force is manipulated to control the external force applied to the helicopter during contact with an object. Since helicopters have strong nonlinear characteristics, a sliding mode controller is designed, and its validity is verified by simulation and an experiment. The results indicate that the sliding mode controller achieves better performance than a linear feedback controller with an inverse system linearization or a multiple loop linearization.

Safety and general versatility are necessary for robots to perform various tasks in human living area. There are tendon based manipulators with nonlinear springs as a manipulator for the requirement. Tension distribution which converts from joint space to tendon space are necessary to control such tendon mechanisms. A conventional tension distribution method using pseudo inverse matrix or inverse matrix of jacobian can not consider tension limits. On the other hand, advantages of structures utilizing bilogical extremities attract much attention. In this paper, we focus on an advantage of musculoskeletal model which contributes to simple algebraic calculation when deriving tension commands. And we develop a tension distribution method which can consider tension limits for musculoskeletal model of biological extremities. Its effectiveness as a part of whole control system is verified by simulations.

A fuzzy decision-making system for multi-criteria robot motion planning and control is described for a constant speed omni-directional mobile robot with active stereo cameras capable of panoramic viewing. The robot can be commanded to move to a target point through an unknown environment while satisfying multiple criteria. Advantages of the proposed method are confirmed by simulation. A multi-agent approach is also described for path planning with multiple robots.

The authors propose robot force control strategies that are robust against disturbance and parameter variation. These strategies are expansions of a disturbance observer which estimates disturbance and parameter variations of motors with a simple computation. Observers are proposed to estimate parameter variations of the environment on which the force is imposed. Since the control system is fixed to a nominal system by the observer, a second derivative of force can be controlled. Force control is introduced using a controller of the second derivative of the force. The force response similar to the force command is realized in spite of the disturbance and the parameter variations of the control object. The effectiveness was confirmed experimentally.>

The authors propose a simple high-performance control strategy based on disturbance compensation by the disturbance observer in task space. The disturbance observer makes robot manipulators linear in task space and realizes acceleration control. The inverse kinematics routine can be simplified, because the disturbance observer compensates not only the disturbance but also the error due to the simplification of the inverse kinematics routine. The strategy was applied to a three-degree-of-freedom direct drive robot to show its effectiveness experimentally.>

A simple high-performance hybrid position/force control that is based on the acceleration tracing orientation method (ATOM) is proposed. From the analysis of ATOM, it is pointed out that precise acceleration control is a key to improve the performance of the motion of the robot. The realization of a strict acceleration controller, however, is almost impossible by the conventional disturbance compensation methods. Recent research on a disturbance observed shows the realization of the acceleration controller. Compared with the inverse dynamics, the observer is simple and robust against parameter variation. Moreover, the disturbance observer can perform parallel computation in each joint by the same algorithm. ATOM was applied to a three-degrees-of-freedom robot to show the effectiveness of the ATOM experimentally.>