Showing papers in "Journal of System Design and Dynamics in 2011"

Power-Assist Glove Operated by Predicting the Grasping Mode

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.

Design and Development of Cylindrical MR Fluid Brake with Multi-Coil Structure

Abstract: Magnetorheological fluids (MRF) are functional fluids which respond to an applied magnetic field with a change in rheological behavior. The objective of this study is to clarify an effective design method to develop the cylindrical MR fluid brake (cylindrical MRB). Before getting into the design, a testing cell to evaluate rheological properties of the MRF was developed. The experimental result was modeled as a characteristic curve which is independent of the shear rate. This model was utilized as fundamental data for design. A cylindrical MRB whose maximum torque is 10 Nm was also designed, and its braking torque was compared with the estimated torque with finite elemental method software for a magnetostatic analysis and proposed mathematical model of the MRF. Although the results show errors at off-state of the brake that come from a friction of an oil seal, the cylindrical MRB whose maximum torque is about 10 Nm was developed.

Enhancement of External Damping of a Flexible Rotor in Active Magnetic Bearings by Time-Periodic Stiffness Variation

Abstract: Previous theoretical studies have shown analytically and numerically that a vibrating system can be stabilised and its vibrations can be suppressed by an open-loop control of a stiffness parameter, a stabilisation by parametric stiffness excitation. This approach is investigated further numerically and implemented experimentally for a flexible rotor with multiple disks supported by active bearings. A periodic open-loop control of the stiffness coefficients of a bearing is realised by periodically changing the control parameters of an active magnetic bearing. This periodic variation of control parameters is regulated at fixed frequency and amplitude in such a way that it acts like a parametric excitation in the rotor system. As it was shown for simple vibrating structures (chain mass system, cantilever, Jeffcott rotor), a periodic variation can enhance the effective damping which leads to a vibration reduction in a vibrating system. Since this control is open-loop, it can be operated in parallel to existing and well-established controllers already in use in active magnetic bearings.In this paper, the method of damping by parametric excitation is realised experimentally in a rotor system. Direct numerical simulation is performed to calculate ranges for control and system parameters where damping by parametric excitation is effective. First experimental results are shown to demonstrate the applicability of the method.

LMI Approach to Robust Control of Rotary Cranes under Load Sway Frequency Variance

Abstract: Because horizontal motion of a rotary crane generates undesirable two-dimensional load sway, skillful operators are needed to control the crane's motion; for this purpose, various types of control schemes have been proposed. Because natural frequency of the rope-load oscillation system affects the stability and performance of the control system, the controller design should consider robustness with respect to rope length. If the control system considers the effect of rope length variance, the crane's motion can be controlled without a sensor system for measuring it. This paper presents a control method based on linear matrix inequality optimization for achieving robustness with respect to rope length variance. Numerical simulations and experimental results demonstrate the effectiveness of the proposed method.

Development of traction control for hauling locomotives

Abstract: As heavy haul trains continue to push the limits of train size and mass and maximise locomotive performance, improving control of adhesion and slip will continue to be in demand. In considering the need to realise maximum adhesion forces for a rail vehicle, it is important to provide the development of new algorithms for traction control in a proper way that takes into account the need to avoid rail and track damage. This paper presents a strategy based on the Polach contact model for the detection of maximum adhesion force, and this strategy also includes slip compensation. The proposed traction control system has been verified by means of a co-simulation approach between the Gensys multibody code and the Simulink package.

Suppression of Two-Dimensional Load-Sway in Rotary Crane Control Using Only Horizontal Boom Motion

Abstract: Horizontal motion of booms in rotary cranes typically generates undesirable twodimensional load-sway; therefore, crane operators must be highly skilled to control the crane’s motion. To reduce the burden on human operators, automatic control systems that can simultaneously control the boom’s position while suppressing unwanted loadsway have been widely investigated. In most existing control schemes, both horizontal and vertical boom motion must be used to suppress load-sway. However, it would be less energy intensive and indeed safer if a control scheme could be developed that only utilized horizontal boom motion, i.e. without the need for any vertical motion. In this paper, we present a nonlinear controller design that enables both boom positioning and load-sway suppression using only horizontal boom motion. Numerical simulations and experimental results demonstrate the effectiveness of the proposed method.

Robotic Mapping and Localization Considering Unknown Noise Statistics

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.

Attitude Control of Small Electric Helicopter by Using Quaternion Feedback

Abstract: In this study, a nonlinear attitude controller for a small unmanned electric helicopter is designed by using quaternion feedback provided by the backstepping control method. First, a quaternion-based multi-input multi-output(MIMO) nonlinear attitude model of a small helicopter is derived. This nonlinear model consists of three parts, namely, the time derivatives of the quaternion, the Euler equation of rotation, and the flapping dynamics of the main rotor and the stabilizer bar. Next, a nonlinear MIMO controller that calculates the desired torque input by the backstepping control method is designed. The control law is modified to exclude a online computation of time derivatives of sensor output. The controller achieves the asymptotic stability of the origin of the attitude error system, and guarantees that the helicopter could track arbitrary desired attitude. Finally, a simulation and experiment are performed, and the results of this simulation and experiment show the effectiveness of the suggested nonlinear MIMO controller.

Adaptive Impedance Control with Compliant Body Balance for Hydraulically Driven Hexapod Robot

Abstract: This article described on the implementation of impedance control with the adaptive elements and compliant walking mechanism in hydraulically driven hexapod robot named COMET-IV. The main issue when applying impedance control in this robot is the body attitude stability during walking on the uneven terrain that contains of major soft surface. The impedance controller is derived for each leg from vertical motion changes. In addition self-tuning stiffness method is proposed as an adaptive element from the changes of the robot's body attitude vector (magnitude), to ensure the robot is self-adapted with the changes of stepped ground. On the other hand, compliant walking mechanism is designed for force-based walking trajectory and proposed impedance controller integration. The proposed controller and mechanism are verified by running the robot on the designed uneven terrain (extremely soft surface) in the laboratory using critical condition of side walking setting.

Fuzzy Inverse Model of Magnetorheological Dampers for Semi-Active Vibration Control of an Eleven-Degrees of Freedom Suspension System

Abstract: A semi-active controller-based Fuzzy logic for a suspension system with magnetorheological (MR) dampers is presented and evaluated. An Inverse Fuzzy Model (IFM) is constructed to replicate the inverse dynamics of the MR damper. The typical control strategies are Linear Quadratic Regulator (LQR) and Linear Quadratic Gaussian (LQG) controllers with a Clipped optimal control algorithm, while inherent time-delay and non-linear properties of MR damper lie in these strategies. LQR part of LQG controller is also designed to produce the optimal control force. After that the LQG controller and the IFM models are linked to control strategy. The effectiveness of the IFM is illustrated and verified using simulated responses of a full-car model. The results demonstrate that by using the IFM model, the MR damper force can be commanded to follow closely the desirable optimal control force. The membership functions of IFM tuned by the results of Clipped optimal strategy. The results also show that the control system is effective and achieves better performance and less control effort than the optimal in improving the service life of the suspension system and the ride comfort of the car.

Compact High Dynamic 3 DoF Camera Orientation System: Development and Control

Abstract: This paper reports on the development and control of a compact, high dynamic camera orientation system with three degrees-of-freedom (DoF). The system orients a small camera around its pan, tilt, and roll axes, using a parallel kinematics driven by ultrasonic piezo-actuators. To fit its application as part of a gaze-driven head-mounted camera system (EyeSeeCam) or as an artificial eye for humanoid robots, the camera orientation device was designed to be small in weight and size as well as to replicate the high dynamic movements of the human eye. The mechanical setup is described and the closed loop control architecture, including a dead zone compensation for the actuators, is introduced. Control experiments conducted with the prototype demonstrated that the system performance is comparable to and even exceeds that of the human oculomotor system.

Motion of a Submerged Tether Subject to Large Deformations and Displacements

Abstract: This paper deals with the motion of a submerged tethered system subject to large deformations and displacements. A tethered system usually employs a cable or wire rope to tether an attached piece of equipment to the ground or to a vehicle, e.g., a remotely operated vehicle (ROV) in the sea. The motion of a tether was modeled using the Absolute Nodal Coordinate Formulation in which absolute slope of elements are defined as nodal coordinates. Herein, this formulation is adapted to account for hydrodynamic drag, buoyancy and added mass. By using the slope coordinates, the hydrodynamic drag acting on the curved shape of the deformed elements can be accurately calculated. Three kinds of experiment were conducted into the fundamental motion of the submerged tether when subject to large deformations and displacements. The numerical results from the proposed model agreed well with the experimental results.

Stability of the Two-Wheeled Inverted Pendulum Vehicle Moved by Human Pedaling

Abstract: In order to tackle with the problems surrounding the environment, the aged society and the individual mobility right, the new type of vehicle which is compact and convenient is expected to be developed. The authors have been investigated such a vehicle called Personal Mobility Vehicle (PMV), which is friendly for human and the environment. In this paper, we proposed the two-wheeled inverted pendulum vehicle moved by human pedaling. The basic mechanism of this new vehicle consists of the system of the stabilization control for inverted pendulum and the pedaling torque by a human. This system has following benefits. By adding the human power, the battery is used for longer time. It is a healthy vehicle due to the pedaling and the seating style makes the driver longer travel than standing. From the academic point of view, it is very important to investigate the interaction with the control of the two-wheeled inverted pendulum vehicle and the human motion. We analyzed the two types of the drive system. One is the mechanical drive system and the other is the electric drive system. The mechanical drive system has the chains between the gear at the pedal and the gears at the wheels. The in-wheel motors are used for the stabilization. As for the electric drive system, the electric generator generates electricity by pedaling and the produced energy is stored by the battery. The in-wheel motors are rotated by the electricity comes from the battery. In the numerical simulation, the vehicle is stabilized by an optimal controller. The influence of the constant pedaling torque and variable one on the stabilization control were compared. It was shown that the variable pedaling torque became the disturbance to the inverted pendulum vehicle and the torque for the stabilization would be necessary according to the disturbance. Therefore, it is found that the electric drive system which drives the in-wheel motors by the less varying torque command from the battery is more effective than the mechanical drive system that directly convey the human power to the wheels. Finally, we confirmed the basic motion of the proposed vehicle by using the prototype vehicle. The vehicle was successfully stabilized by the controller and moved by the human pedaling.

Analysis of Feed-Forward Control Design Approaches for Flexible Multibody Systems

Abstract: End-effector trajectory tracking of flexible multibody systems is a challenging task. In this paper feed-forward control designs based on quasi-static deformation compensation and exact model inversion for end-effector trajectory tracking are presented. They are combined with a simple feedback strategy and tested by simulation of a very flexible two arm manipulator. With both approaches good results for end-effector trajectory tracking are obtained. It is shown that a significant improvement of the inverse model approach is achieved by including the elastic rotation of the first arm in the system output description. This yields the far best accuracy of the tested approaches.

Study on Active Vibration Control for High-Speed Elevators

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.

Modeling and Vibration Analysis of Flexible Robotic Arm under Fast Motion in Consideration of Nonlinearity

Abstract: This paper deals with a problem of modeling and vibration analysis of a flexible robotic arm under fast motion. Conventional method of modeling does not exactly express the bending mechanism of a flexible beam. Then a new description of deformation on the flexible shaft and Hamilton's principle are used to derive the dynamic model of the flexible robotic arm. A nonlinear dynamic model is proposed to describe the dynamic behavior of the flexible beam and the dynamic equations of the flexible robotic arm are also presented. Derived equations consist of some nonlinear forces and nonlinear stiffness. The present research considers the effect from those nonlinear forces coupling with angular functions (angular position, velocity, acceleration). A forced vibration method is applied to evaluate the characteristics of flexible vibration. In this research, numerical calculations based on two strategies are applied to analyze the flexible vibration. In the first strategy (AIM, angle independent method), angles of joints are assumed to be independent of the external forces. In the second strategy (ADM, angle dependent method), the effect on the angular functions of joints due to the external forces is considered. Especially, the gravity affects significantly on the residual vibration of flexible robotic arm and on the angular functions.

Numerical Simulation of Tire Behavior on Soft Ground

Abstract: The purpose of the present study is to develop a three-dimensional efficient interactive model and a numerical procedure to simulate a tire on soft ground, which can be applied to multibody dynamics for off-road vehicles. For motion analysis of the tire on soft ground, it is necessary to describe the elastic deformable behavior of the tire and the behavior with large displacement and local disruption of soft ground. A three-dimensional analysis must be conducted in order to express the complex behavior of the tire on soft ground due to the deformation of the tire and the landform of soft ground, such as ground heaving in the vicinity of the tire side edge. As the tire model, we adopt a distributed lumped mass-spring model, in which a rigid wheel is connected to a number of tire-masses by Voigt elements. This tire model allows us to describe the local deformation of the tire and the distributed contact pressure between the tire and soft ground. In addition, as the soft ground model, we adopt a discrete element (DE) model, in which soft ground consists of a number of rigid soil particles. This ground model allows us to express the discrete behavior of soft ground. Furthermore, the contact between the tire and the soft ground is defined as the contact between the tire patches constructed of tire-masses and the soil particles of soft ground. Numerical simulations of the tire behavior on soft ground have been carried out under several conditions using the proposed model. The numerical results revealed that three-dimensional motion analysis of the tire behavior on soft ground is possible, and that the proposed model and the numerical procedure could be validated through comparison with previous experimental results on the tractive and cornering performance of the tire on soft ground.

Giant Swing Motion Control of 3-link Gymnastic Robot with Friction around an Underactuated Joint

Abstract: This paper discusses a control method which can stabilize the giant swing motions of 3-link horizontal bar gymnastic robot. A method called Multiple-prediction Delayed Feedback Control(MDFC) proposed by the authors, which has been shown to be effective in control such chaos system, is extended in this paper to experimental gymnastic robot system, taking in account the effect of friction around the link joint. The dynamic of underactuated systems like gymnastic robot shows significant differences in cases of with friction and without friction. However, MDFC considers only the ideal situation without friction. Therefore, a stabilization control method consisting of three kind of control inputs which the one is MDFC for guaranteeing asymptotic stability and the others are used for friction compensation is derived. Numerical simulations and experimental results prove its effectiveness of our proposed method.

Force Sensorless Impedance Control of Dual-Arm Manipulator-Hand System

Abstract: In this paper, we describe the manipulation of nuts and flexible objects for assembly work by incorporating force sensorless impedance control in a robot. This robot is a dual-arm manipulator, and each of its end effectors is a three-fingered robot hand. Generally, a force sensor is used for recognition of external force on the fingertips. However, such sensors are very expensive and easily damaged by inappropriate contact with the object. This motivated us to estimate the external force without using a force sensor. In this study, the external force on the robot fingertip was estimated using a disturbance observer. Then, estimated results were compared with measurement results of the force sensor to validate the former. Impedance control was designed for a three-fingered robot hand by using this estimated external force. By application of the designed impedance control to the robot hand, the robot was successfully able to grasp nuts ranging in size from 2 mm to 12 mm through an algorithm formulated in the study. In this algorithm, we incorporated a method called following control to retain the contact of the finger with the worktable while performing the grasping task. Thus, the nut grasping task could be performed at a higher success rate, despite some errors in the robot position and vision data. Furthermore, a boiled egg considered as a flexible object was successfully grasped through force sensorless impedance control. An impedance controller for the boiled egg was designed using identified model parameters of the egg, and its effectiveness was validated experimentally.

Control of Differential Air and Hydrogen Pressures in Fuel Cell Systems

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.

Development of a Standing Style Transfer System ABLE with Novel Crutches for a Person with Disabled Lower Limbs

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.

System Identification of Railway Trains Pantograph for Active Pantograph Simulation

Abstract: High performance of the contact wire and pantograph dynamic interaction is required in the operation of high speed railway vehicles. Due to the constraint of field test, simulation and lab experiment procedures are performable to verify the interaction. Such simulation needs accurate modeling of the response of the pantograph for the consistency in prediction and control. A simple system identification of the pantograph is executed based on the lab experimental data using commercial software and least squares method. The validation of the procedure is performed through comparison between extended experimental data and numerical simulations of the pantograph system. Further analysis is by applying active pantograph control on the system by simulation. The results show availability of the design for active pantograph system.

Identification of the Exponential Function Type Nonlinear Voigt Model for Sports Surfaces by Using a Multi-Intensity Impact Test

Abstract: The purpose of this study is to propose a nonlinear viscoelastic model for sports surfaces and an identification method of this model. Although various models have been proposed to represent the behavior of rubber materials, some models represent only the material’s elastic behavior, while other models deal with viscoelastic behavior but have problems in the computer simulation of that behavior. The model proposed in this study can represent viscoelastic behavior well and also has stability of computer simulation. In the identification methods, four types of drop weights, which have different mass and damping material for producing a wide range of impact durations and impact intensities, are used for impact tests. The impact force, velocity and deformation are measured in each impact test, the parameters of the elastic element of the model are calculated by the least squares method and then the parameters of the viscous element of the model are calculated from the experimental force and the estimated force produced by the elastic element. The model proposed in this study has high identification accuracy and stability of simulation compared to previous models.

Realization and Application of the Base Plate Jerk Feedback in a Pneumatic Positioning Stage

Abstract: In this paper a pneumatic positioning stage which is mounted on the base plate and supported by the coil-type spring isolators is considered. The stage is moved by the driving force during positioning and the reaction force causes vibration of the base plate with its natural frequency, which degrades the performance of the positioning. To reduce the effect of the reaction force and improve the positioning time, the base plate jerk feedback is proposed. An external force is used to realize the principle of the base plate jerk feedback based on the theoretical background. The experimental results confirm that the working principle of the base plate jerk feedback obeys the theoretical concepts. The feedback is then employed for the real positioning. Based on the experimental results including repeatability, the effect of the reaction force was considerably reduced and the settling time of the response was improved, after employing the base plate jerk feedback with approximate optimal gain.

Physical Fatigue Comparison of Eco-Driving and Normal Driving

Abstract: Nowadays, eco-driving as a series of driving behaviors is proposed to reduce CO2 discharge of vehicle and realize safe driving. The eco-driving behaviors are mainly about accelerator and brake works that are operated by leg`s motions of driver; however, there are few studies to explain physical fatigue resulted by leg`s motions for eco-driving behaviors. In the paper, eco-driving experiment was conducted in the modes of normal driving, eco-driving with instruction, and eco-driving with eco-indicator. The simulated driving experiment was realized by a universal driving simulator system, and surface electromyography of leg muscle of 10 subjects was measured to clarify physical fatigue of driver in different driving modes. The experiment indicates that fuel economy in eco-driving with eco-indicator is higher than other driving modes, and muscle activities are lowest by signal analysis of the surface electromyography. The result also suggests that eco-indicator is effective assistant system to help driver realize eco-driving as well as reduce physical burden of driver.

Development of a Generation Mechanism of Synchronous Vibration Suitable for Hand-Held Vibrating Tools: Investigation of an Impact Model with Two Oscillators

Abstract: The hand-arm vibration syndrome characterized by Raynaud's disease is caused by long-term use of hand-held vibrating tools. The purpose of the present research is to develop a new vibrating tool using self-synchronization phenomena in order to reduce hand-arm vibration. In the present paper, an elementary model with a generation mechanism of synchronous vibration suitable for a tamping rammer used to compact cohesive soils on the ground is developed. This model consists of upper and lower blocks coupled by coil-springs, and two rotor-type oscillators are mounted individually on the lower blocks. The nonlinearity due to the impact behavior between the lower block and the ground is approximated by piecewise linear characteristics. The synchronized solutions and the stability are analyzed by applying the improved shooting method for impact vibration analysis. Analytical and experimental results confirm that stable synchronized solutions which are able to achieve a good balance between vibration control and excitation exist. In addition, it is proven that the existence region of the stable solutions can be expanded by setting the system parameters appropriately.

Decomposed Dynamic Control for Flexible Manipulator in Consideration of Nonlinearity

Abstract: A model of a flexible manipulator is developed with considering the geometrical nonlinearity and the effect of gravity. The model can be divided into a flexible dynamic subsystem and a rigid dynamic subsystem, and a decomposed dynamic control (DDC) including flexible dynamic control and rigid dynamic control is proposed for a controller design of the flexible manipulator. The flexible dynamic control has been investigated for a desired trajectory using an optimization, and the optimization is valid method to deal with nonlinear problems but dependent on the accuracy of models. There are errors in models and other factors causing disturbances inevitably, so that the rigid dynamic control is expected with enough robustness to overcome the uncertain problem. In this paper, the proposed controller does not only track the desired trajectory, but also further suppresses the residual vibration to improve performance of control. A hybrid sliding mode control (HySMC) is proposed to track the desired trajectory and provide a compensator for further vibration suppression. This paper mainly presents the theoretical design and experimental verification of the proposed controller.

Movable Range-Finding Sensor System and Precise Automated Landing of Quad-Rotor MAV

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.

Driving at Resonance Point of Multi-Degree-of-Freedom System by Decentralized Control

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