The present paper describes the attitude control of a small UAV using a flow sensor system. The installed flow sensors measure the flow field characteristics around the wing, which are sensitive to the attitude of the airplane. The dynamics of the responses of the flow sensors to the attitude variation were identified in dynamic wind tunnel experiments, and the obtained dynamic model related the flow sensor output to the airplane attitude. The attitude of an airplane was then controlled by the elevons so that the desired flow sensor output was attained, resulting in a maximum lift coefficient. The controller was designed using the H_∞ control method with sufficiently robust stability. Numerical simulations and actual flight tests were conducted, and effective control of the airplane attitude using the small flow sensors was demonstrated.

View full abstract

The accuracy of small and low cost GPS is insufficient to provide data for precisely landing Micro Air Vehicles (MAV)s. This study shows how a MAV can land on a small targeted landing site by using sensors rather than imprecise GPS data. This paper describes a proposed movable range finding sensor system for measuring the environment and an algorithm of position measurement. This range finding system consists of four Infrared (IR) sensors, four servo motors and one ultrasonic sensor. In order to measure the MAV's position, the sensor system vertically swings each IR sensor using the servo motors and these IR sensors detect the edge of landing target. And this sensor system calculates the position from the measured edge direction and the ultrasonic altitude. Additionally, experiments of autonomous hovering over a 52cm × 52cm table and autonomous landings were carried out indoors using the proposed sensor system. Our experiments succeeded, and as a result, the MAV kept flying horizontally within a 18cm radius circle, and then it landed on the table from a height of 50cm. The IR sensors were selected because of the payload limitations of small MAVs. If the MAVs' payload capacity were higher than a laser sensor, then it would be used, since the lasers can operate better in sunlight than IR sensors and also they tend to have longer scanning ranges and are more accurate.

View full abstract

Control Moment Gyroscope (CMG) has been expected to be applied to a spacecraft such as an earth observation satellite in recent years. However it is not easy to control it because CMG has a singularity condition and a major source of disturbance. Although there are many singularity avoidance logics, these optimal methods from the viewpoint of singularity avoidance may cause inner disturbance by fast and furious motion of gimbals in avoiding singularity. This paper presents a new but simple CMG steering law using preferred initial gimbal angles and null motion for high accurate attitude control system on an agile spacecraft. The preferred initial gimbal angles are decided by evaluating function considering inner state of CMG. From the simulation results, the effectiveness of the proposed method was verified.

View full abstract

This paper studies the behavior of the giant swing motions of a 3-link horizontal bar gymnastic robot using the delayed feedback control (DFC). A modified DFC method called Multiple-prediction Delayed Feedback Control (MDFC), which controls the chaotic system via periodic gain is proposed in this paper. First, plural Poincaré maps are defined to regard the target continuous-time system as a T-periodic discrete-time system, so that the system stability can be evaluated based on the theory of monodromy matrix. Second, a way to calculate analytically the error transfer matrix and the input matrix which are necessary for discretization is presented. Finally, simulation results show that our proposed method is effective in the control of the giant swing motions.

View full abstract

The dynamic performance of a permanent magnet synchronous motor (PMSM) is influenced practically by uncertainties in parameters including external load disturbance and inertia variation. This paper presents robust control to maintain dynamic performance of a PMSM with system inertia variation and external disturbance effects. The proposed algorithm used an extended Kalman filter (EKF) to identify system inertia accurately and then tuned the parameters of the speed controller. Furthermore, the estimated inertia is sent to adjust the reference model of the disturbance observer, and the estimated disturbance torque is fed forward to adjust the electromagnetic torque reference simultaneously. Both control units, system identification and disturbance observer, adaptively correct each other's estimated parameters. The proposed speed control scheme is implemented on a PMSM driver by a digital signal processor (DSP) platform, and the performance effectiveness is verified through MATLAB/Simulink simulations and experiments. To confirm its validity, the proposed speed controller is also compared with an industrial PMSM controller in real-time experiments under different practical conditions.

View full abstract

This paper presents an analysis of H_∞ Filter(HF) for Robotics Mapping and Localization with unknown noise statistics. HF which is also known as the minimax filter is proposed in this paper to estimate the robot and landmarks location while robot moves through an unknown environment. Some of the conditions are proposed to ensure that the state covariance in HF is converging to a steady state value. Furthermore, the analysis of HF convergence for a robot observing landmarks are presented to examine its behavior through the observations. From the experimental results, HF gives a sufficient estimation about the environment. Subsequently, such a result can provide other available estimation methods with the capability to ensure and improved estimation in robotic mapping and localization problem.

View full abstract

A standing style transfer system, ABLE, is designed to assist a person with disabled lower limbs to travel in a standing position, to stand up from and sit down in a chair, and to go up and down steps. The ABLE system comprises three modules: a pair of telescopic Lofstrand crutches, a powered lower extremity orthosis, and a pair of mobile platforms. In this paper, the telescopic Lofstrand crutch is mainly discussed. This crutch has no actuator, and its length is switched between two levels; it assists the person when standing up and sitting down in the short length state, while it maintains the body stability in a standing position when traveling in the long length state. The experimental results related to the traveling in the standing position and standing up motion confirm the design's effectiveness.

View full abstract

A control algorithm that estimates human grasping intention is developed for driving the Power-Assist Glove that assists grasping force. In order to operate the Power-Assist Glove with appropriate drive mode, we focused on finger-joint angles in the process of grasping. There is shown to be a correlation between the three principal grasping modes and the initial movement patterns of the finger-joint angles. To distinguish the patterns and predict each mode, a pattern classification method is applied to the algorithm. The control system achieved an 80% success rate in distinguishing the grasping modes of people. The Power-Assist Glove features a simple drive mechanism using soft actuators and decreases the muscle activity that corresponds to 1.5 kg loads.

View full abstract

This paper describes a method of configuring a control system for keeping the differential pressure of the hydrogen and air supplied to a fuel cell within a specified range. The proposed method assumes that the control system of the air pressure and mass flow rate is based on the use of a mathematical model, whereas the hydrogen pressure control system does not employ a mathematical model and treats the consumption of hydrogen during power generation as a disturbance. When hydrogen consumption due to power generation is treated as a disturbance, the responsiveness of the hydrogen pressure and air pressure varies depending on the amount of power being generated. Therefore, the air pressure is predicted using transfer functions and the hydrogen pressure is made to follow the predicted value. In addition, the air pressure is made to follow the larger of either the reference pressure or the hydrogen pressure. This paper first describes the derivation of the mathematical model of the air supply system. The mathematical model is then used to design a sliding mode control system based on the two variables of the air pressure and mass flow rate. The method of configuring the differential air and hydrogen pressure control system is then explained, and experimental results are presented to validate the proposed design method.

View full abstract

In this study, the authors aim to develop a small gas engine system for biomass gas by modifying the control system of a conventional spark ignition engine. Before developing a control algorithm, combustion experiments with various component fuels assumed to have the components of real biomass gases, such as fermentation and pyrolysis gases, were carried out. It was clarified that the relationship between dimensionless combustion duration and equivalence ratio can be expressed by a first-order linear function regardless of fuel composition. Indicated thermal efficiency can also be expressed by combustion duration and volumetric efficiency when the coefficient of variation of indicated mean effective pressure is lower than 5% and pumping loss decreases against volumetric efficiency linearly, and the relationship between combustion duration and MBT can also be expressed by a first-order function. By using these relationships, a gas engine control algorithm, which can define the target values of the equivalence ratio of a premixture and ignition timing that realize a high thermal efficiency for fuel compositions automatically by analyzing in-cylinder gas pressure data in real time, is developed in order to use gaseous fuels produced from biomass resources effectively. Thus, a biomass gas fuel engine system is developed by applying the algorithm to an automobile gasoline engine, hardware modifications of which are only the fuel supply system and flywheel. The engine system is connected to a gasification plant using wood chips and an operation test is carried out. As a result, the engine system can set an optimum premixture condition and an ignition timing, which realizes a stable and high-thermal-efficiency operation automatically.

View full abstract

This paper presents optimal trajectory planning and iterative learning control for a throwing manipulation which can control not only the position but also the orientation of a polygonal object robustly to uncertainties by low-degree-of-freedom robotic arm. We show experimentally the validity of the proposed method with the one-joint robotic arm. We also demonstrate the usefulness of the throwing manipulation by applying it to the parts assembly and sorting on experiments.

View full abstract

A new control device is proposed to isolate an elevator cabin from irregularities on a guide rail. The device consists of two rotary electric motors with disks and eccentric masses. One motor produces torque to rotate the eccentric mass according to the command signals from the controller for horizontal control, while the other rotates the mass to eliminate the unwanted vertical force. To design the optimal controller to reduce the horizontal vibration of the cabin, the dynamics of the cabin, including the proposed control device, are described by a linear equation. The performance of the proposed control system is examined through numerical simulations taking into consideration the nonlinear characteristics of the rotating masses, which are neglected in designing the controller, and through experiments with a miniature elevator cabin carrying the proposed actuator. The results indicate the proposed control device reduces the horizontal vibration without producing the unwanted vertical vibration.

View full abstract

When elevators travel at high speed, horizontal vibrations of the car tend to occur due to guide rail deformations, deteriorating ride comfort. Therefore, several active control systems have been developed to reduce these vibrations. These systems consist of six actuators, which independently move the guide rollers. To reduce costs and installation time, it is necessary to develop a system with a minimum number of actuators and a simplified controller. We developed a system with only three actuators. The controller incorporates an H-infinity control design method for maintaining stability of the system when there is a change in load. Furthermore, from a practical point of view, it is important to reduce the order of the controller so that the time for on-site parameter tuning can be reduced. Therefore, we reduced the H-infinity controller to a P controller. We demonstrated that the maximum amplitude of vibrations of a car with active control system can be reduced to almost half the vibration amplitude without control.

View full abstract

A control method has been developed to always excite a multi-degree-of-freedom system efficiently at a resonance frequency. When an excitation point corresponds to a vibration detection point in the multi-degree-of-freedom system, a phase lag at a resonance frequency and a phase lead at an anti-resonance frequency alternately appear in the vibration characteristics, and the phase lag becomes 90° at all the resonance frequencies. Therefore, if a controller that has a phase lag of 90° and a constant gain in a wide frequency range is used, self-excited vibration is generated at all the resonance frequencies. The self-excited vibration controller can be expressed as the sum of the positive velocity feedback control with a high gain in a high frequency domain and the integral control of the displacement with a high gain in a low frequency domain. A local feedback controller for each actuator consists of a self-excited vibration controller, a saturation element that limits excitation force, and a negative velocity feedback controller that provides damping. A driving at a resonance point system using many actuators with local feedback control, that is, decentralized control, is excellent in its adaptability to the environment, in its extendibility, and in its fault tolerance. In addition, the self-excited vibration mode can be freely switched on by changing the frequency of the sine wave that causes the self-excited vibration.

View full abstract

To clarify the mechanism of observed violent vibration of a brace adjacent to a high circular stack, an experimental study was performed. The experimental apparatus consists of a vertical elastic rod placed close to a large solid cylinder. Accordingly, airflow makes the rod whirl at its first natural angular frequency. Whirling motion grows as airflow velocity increases. Whirling direction depends on the relative location to the cylinder and not on airflow velocity. Further, analytical study was done by assuming the flow past cylinder is frictionless, irrotational and incompressible. Analytical results show fairly good agreement with experimental ones as well as the actual brace vibration.

View full abstract

A pressure wave propagating in a tube often changes to a shock wave because of the nonlinear effects in the propagation medium. The purpose of this study is to establish a practical analytical model to analyze this phenomenon. In previous reports, a concentrated mass model was proposed to analyze nonlinear pressure wave phenomena in a straight cylindrical tube. In the present paper, models of enlargement and contraction are proposed. The models of the enlargement and contraction elements consist of masses, nonlinear springs, base support dampers, and nonlinear dampers. The nonlinear damper is derived from the pressure loss at the enlargement and contraction. To confirm the validity of the proposed model, an experiment on a sound tube with an expansion-chamber muffler is performed and the experimental results are compared with the numerical results obtained by the concentrated mass model. The numerical computational results agree well with the experimental result. Therefore, it is concluded that the proposed enlargement and contraction models are valid for the numerical analysis of nonlinear pressure wave problem in a tube with an expansion-chamber muffler.

View full abstract