This paper presents a novel congestion controller for transmission control protocol/active queue management (TCP/AQM) networks. In order to maintain the queue length to a value less than the buffer size at the aggregation nodes, the queue management mechanism drops some packets depending on the probability calculated by a congestion controller. However, conventional controllers such as random early detection (RED) algorithms and proportional-integral-derivative (PID)-based controllers are not compatible with parameter variation in TCP/AQM networks. Parameter variation in TCP/AQM networks includes the change of the number of TCP connections, the inflow of user datagram protocol (UDP) flows and so on. In the proposed method, the effect of parameter variation is estimated as drop probability disturbance by using a disturbance observer (DOB). By using the DOB, disturbance suppression characteristics of the controlled system can be drastically improved. In addition, the TCP/AQM network system is analyzed on the basis of an acceleration control scheme. The proposed method is validated by simulation studies performed using a nonlinear model of a TCP/AQM network and verifications made using the network simulator ns-2.
In procedures that involve remote control, such as remote surgery, it is necessary to operate a robot in a remote location in a sensitive environment; the treatment of internal organs is an example of such a procedure. In this paper, we propose a method for autonomous hazard avoidance control that is based on information on the contact environment. The proposed method involves the use of bilateral control. During safe operations, systems are controlled by bilateral control. During dangerous operations, a slave system is controlled autonomously so as to avoid dangerous operations. In order to determine the degree of operation risk, fuzzy set theory is applied to the force exerted on the environment. Further, variable compliance control based on the force exerted on the environment is utilized to avoid the risk. The effectiveness of the proposed method is confirmed by experimental results.
Recently, there has been an increase in the demand for container cranes capable of automatic operation. Anti sway control techniques essentially require a sway sensor for achieving good control performance through a feedback signal. However, the use of a vision system to detect the sway angle results in the deterioration of control performance owing to the influence of weather and delay in detection. In this paper, we describe an effective method for precise state estimation in a system by taking the sensor delay into account. The effectiveness of the observer is verified through various numerical simulations and experiments using a model plant.
The large-scale high-precision scan-stage is industrial equipment for microfabrications. The scan-stage needs not only fast and precise positioning but also the attitude control of the stage. The attitude of the stage is disturbed by the stage thrust in scanning. However, the sampling time of output is much longer than the sampling time of control input by DSP because image sensors are employed in the output encoder. It is difficult to reject the disturbances by single-rate feedback system. In this paper, we proposed the attitude control based on PTC (perfect tracking control) using driving force and surface shape of the stage. Finally, simulations and experiments are performed to show the advantages of the proposed control system.
In this paper, a stability index based on the ZMP (zero-moment point) for biped robots moving on rough terrain is proposed. The proposed method projects a support polygon on to a virtual plane and sets a virtual ZMP on it. In rough terrain, using the proposed method, stability check and trajectory planning are able to be treated as the case of flat terrain. The validity of the proposed method was confirmed by some simulations and experiments.
This paper proposes a real-time image processing system for wheelchair recognition at elevator lobby. This system extracts objects with frame difference method. From the image of extracted objects, heads of people are detected by the Hough transform. Vertical shooting from ceiling improves the performance of people counting since the detected head has high roundness and occlusion of people is prevented. Two feature quantities are introduced to recognize wheelchairs. They are the area value and the ratio of traveling length to vertical length. Since these quantities require a method for drawing the contour line. This paper proposes a new simple method to draw a contour line. The effectiveness of this system is confirmed through experiments.
In bilateral teleoperation, the human operator manipulates the master robot while watching video images that are sent from the slave side. Live video streaming causes a significant communication delay to the system. However, a conventional definition of transparency for bilateral control does not consider this delay. In this paper, a novel definition of transparency is proposed. If perfect transparency is achieved, the visual sense and tactile sense synchronize. This transparency is nearly achieved by applying a compliance control to the slave controller. By using this structure, the slave robot contacts the environment safely even if there exist communication delay between the master side and the slave side. In addition, the visual sense and tactile sense synchronize. The validity of the proposed method is shown by numerical and experimental results.
Recently, various display equipments such as LCDs, CRTs, and projectors have been widely used, and people's interests in image quality enhancement have increased significantly. Common display users are unable to adjust image quality by themselves because they do not have sufficient knowledge about adjusting the image quality. The authors focus a tone reproduction of display, which is one of the important factors for image quality enhancement, and aim to develop an image quality enhancement support system to help the display users adjust the image quality of displays. The system optimizes the parameters that control the tone reproduction on the basis of user's subjectivity or KANSEI. The tone reproduction is controlled by a tone curve that consists of a transformation equation with parameters. The proposed method can reflect human preference; applied interactive evolutionary computation is used as an optimization method. An optimum set of parameters are derived on the basis of human subjectivity or KANSEI using interactive evolutionary computation. This technique is verified by comparing it with the image quality derived manually and the manual derivation time.
Recently, minimally invasive surgery (MIS) has become apparent. Research has been performed on surgical robots needed in MIS. In the case of MIS, it is effective to express environmental impedance as numerical data in order to preserve it for establishing standard reference values of the conditions of internal organs. In this paper, we propose a novel method for the estimation of stiffness in real environments in which bilaterally controlled robots are needed. By using the proposed method, environmental stiffness can be estimated dynamically regardless of the initial position of slave system. The viability of the proposed method is confirmed from the experimental results.
In this paper, a virtual cylindrical screen (VCS) algorithm is proposed for detecting stationary objects inside a VCS when a sensor is moving in the forward direction along its optical axis. Simulations are carried out to investigate the advantages of foveation in the use of the VCS algorithm, and the advantages are discussed by comparing the pinhole camera (PHC) model with the sine curve (SC) model and the advanced wide angle foveated (AdWAF) model. A correction weight function is introduced for estimating the error in the optical flow that is calculated by using each image model. Moreover, the uniform optical flow (UOF) model for the VCS is developed for use in various applications, and an approximate image-height function is formulated for this model. The accuracy of the optical flow corresponding to a point on the VCS is investigated in simulations carried out using the correction weight function.
A stability analysis of force control based on momentum is presented in this paper. The inertial force which makes the robot unstable such as centrifugal and Coriolis force is strictly modeled with this controller. Hence, the stability is improved. This fact is shown by an analytical approach with the transfer function. In order to increase response tracking capability, how to compose force feedforward and disturbance observer with the controller is also considered. The validity of the ways is confirmed by several simulations and experiments.
The electromagnetic field environment around a power semiconductor device is extremely important. This is because it can potentially affect the switching speed and thereby the switching loss of the device. Electromagnetic induction due to switching of devices causes a change in the gate voltage of the devices. This change in the gate voltage during the switching period causes drastic increase in current at short circuit and concentration of switching loss when many devices are connected in parallel. In this paper, we describe the influence of the wiring structure of power semiconductor devices on their switching characteristics using three-dimensional electromagnetic field analysis and circuit simulation. We also describe methods to improve the switching problems caused by the wiring structure of the main circuit and control circuit.
This paper describes a resonant switched-capacitor converter (RSCC) for voltage balancing of several capacitor or battery modules connected in series. This voltage balancing circuit carries an electric charge between the capacitor modules with a soft switching operation, resulting in a reduction in power loss and EMI. Moreover, a phase-shift control method is applied to improve the voltage-regulation performance of the RSCC by applying a voltage feedback control. This paper analyzes the relation between the capacitor currents and the resonant currents in the RSCC. Based on the analysis, a new controller is proposed for a circuit configuration having capacitors more than three. The experimental results confirm the validity and effectiveness of the proposed control method.
This paper proposes the realization of a carrier-based space vector pulsewidth modulation (SVPWM) method using analogue and digital techniques. This PWM method provides unbalanced phase outputs for a two-phase three-leg voltage source inverter (VSI). The principle is fully described. The proposed space vector equivalent phase leg reference voltages are derived from conventional ones. With the proposed SVPWM method, the amplitude of the unbalanced phase voltages can be easily controlled as required whilst the phase difference angle is kept at 90 degrees. This characteristic is suitable for a control method of an asymmetrical type two-phase induction motor. The validity of the proposed method is verified by both calculated and experimental results under a variation of PWM parameters with resistive-inductive and motor loads in terms of space vector equivalent reference waveforms, current waveforms and space vector trajectories and so on.
In teleoperation, the operated objects are often present in an ambient environment such as water or blood. It then becomes difficult to distinguish between the reaction force from the operated objects and the reaction force from the ambient environment. This affects the safety of the operation and the operation itself. In this paper, we propose a control method for reproducing the reaction forces from an operated object, excluding the reaction forces from the ambient environment. We introduced the concept of dynamic reproducibility, which is an ideal condition considering the ambient environment. Furthermore, a bilateral control system that considers the ambient environment is designed on the basis of dynamic reproducibility. The validity of the proposed system is confirmed by the simulation results and the experimental results.
Renewable energy such as wind force and solar light has collected the attention as alternative energy sources of fossil fuel. An energy storage system with an electric double-layer capacitor (EDLC), which balances the demand and supply power, is required in order to introduce the electric power generating system that utilizes renewable energy. Currently, the research and development of these energy storage systems are actively carried out. In the energy storage system with an EDLC, the DC/DC converter having the function of the bidirectional power flow and the buck/boost performance is essential as an interface and power control circuit. There are two types of the bidirectional buck/boost DC/DC converters. One type consists of two buck/boost DC/DC converters with one reactor. The other type consists of two sets of two-quadrant DC/DC converters with one reactor. This paper discusses the comparison of these types of DC/DC converters with bidirectional power flow and buck/boost performance. The two types of DC/DC converters are estimated for their application to the energy storage system with the EDLC. As the voltage endurance of the device is lower and the mean current is smaller in the latter type of converter despite of having twice the number of devices compared to the former, the latter type of converter has the advantage of a smaller reactor, i.e., core volume and loss, and lower loss in the converter.
Renewable energy such as sunlight has recently been receiving much attention. However, it has some problems that a precipitous fluctuation of electric power in the PV-generating system has an adverse affect on electric power systems. This paper presents its short-term forecasting with chaos and the effectiveness in reduction of the energy storage system is discussed.