This paper proposes a method for suppressing the speed vibration caused by the angular transmission error in cycloid gears used in industrial robots. It is important for industrial robots to have high accuracy. However, cycloid gears with an angular transmission error may cause vibration in the arms of a robot. The proposed method for compensating for the speed vibration uses a new extended state observer that is based on a model that considers a cycloid gear with an angular transmission error. A compensation current is generated by using the torque vibration which is converted from the estimated speed vibration. The speed vibration is suppressed using this compensation current. The experimental results show that the proposed system suppresses the vibration at the load speed.
A leg extender exoskeleton is very useful when doing work involving tall shelves, looking around for security, etc. Therefore, we developed an exoskeleton with an active ankle joint. Its weight is approximately 12kg and it extends the leg length by 40 cm. It provides good mobility, and a well-trained person can run with it.
This paper proposes methods based on the zero moment point (ZMP) to compensate for the effects of centrifugal force and facilitate better mobility of wheel-legged mobile robots (WLMRs). A centrifugal force acting on a high-speed WLMR destabilizes the ZMP. Thus, the centrifugal force should be compensated for to realize dynamic behavior. However, there have been few studies on compensating for the effect of centrifugal force acting on a WLMR. This paper discusses control methods to compensate for the effect. New centrifugal force compensation methods based on disturbance preview control and a zero-phase low pass filter are shown. These methods compensate for the effects of centrifugal force and control the ZMP to follow the reference ZMP. The effectiveness of the proposed methods was validated via precise three-dimensional simulations and experiments.
Electric vehicle have become a universally recognized solution for future green transportation. However, the mileage per charge of the EVs is lower than that of internal combustion engine vehicles. In this paper, a model-based range extension control system (RECS) for acceleration and deceleration modes is proposed. In this proposed method, slip ratio, copper loss, and iron loss are considered. The total driving-braking force is distributed based on the vehicle acceleration and velocity. The effectiveness of the proposed method is verified through simulations and experiments.
This paper describes a stabilizing output feedback controller for a time-delay system that is derived from a complete quadratic Lyapunov-Krasovskii functional. Because the complete quadratic Lyapunov-Krasovskii functional contains non-constant coefficients for its decision variables, the stabilizing problem is more difficult to solve than the stability problem. Instead, this paper introduces a null term with a value of zero to convert the derivative of the Lyapunov-Krasovskii functional into a quadratic form and avoid the multiplication of decision variables. The controller design procedure is given by a stability condition based on the linear matrix inequality. The performance of the proposed controller is weighted to consider the dynamics of the controlled plant.
This paper proposes a control method that attenuates adverse effects due to cogging torque on the vibratory system. A conventional controller utilizes a disturbance observer to estimate the cogging torque; however, the observer uses a filter that causes an estimation delay. If the cut off frequency is high enough, the delay may be negligible, but the estimated disturbance (cogging torque) will be contaminated with vibration. Instead, the proposed method uses a filter with a low cut off frequency; the estimation delay is compensated for by the leading angle, then it is used to attenuate the disturbance in the next rotational duration. The experimental results showed that the proposed method was clearly superior: the RMS magnitudes of the velocity control error were drastically reduced.
High-precision stages are implemented in the manufacturing processes for electronic devices such as integrated circuits and liquid crystal displays. The development of electronic equipment manufacturing industry requires increasingly higher levels of integration density; hence, not only stage position but also the stage attitude needs to be controlled rapidly and precisely. The attitude is determined on the basis of roll, pitch, and yaw motions, which are affected by the nonlinearity and coupling arising from Euler's equation and coordinate rotation. These effects degrade the attitude control performance. This paper proposes a multi-input multi-output nonlinear feedforward attitude controller which compensates for these effects. The effectiveness of the proposed approach is verified through simulations and experiments.
This study investigates the scheduling of water flow between water treatment plants and distribution reservoirs. We aim to reproduce the performance of an experienced operator for a water supply system. The steering groups of water supply systems face problems due to the decreasing number of experienced operators. Without the expertise of experienced operators, it is difficult to carry out operations in a safe and stable manner. For this purpose, regression analysis using Partial Least Squares was applied to reproduce the performance of an experienced operator. In addition, the k-means method was applied to cluster predictors for regression analysis. Experimental results show that the root-mean-square values for the reservoir water level obtained using the proposed method were smaller than those obtained using a conventional method and our previously proposed method. Thus, we confirmed that the proposed method is able to acquire operation knowledge from experienced operators, and un-skilled operators can use this data to regenerate an operation plan. This method is expected to compensate for the decrease in the number of experienced operators.
With the decrease of experienced engineers in recent years, studies have focused on developing systems that save skilled hand motions as electronic data for reproduction by robots. However, few studies have succeeded in reproducing skilled hand motions in three-dimensional work spaces. In addition, the reproducibility of a hand motion is not guaranteed when the initial distance between an object and the robot for the saved motion differs from the distance for the reproduced motion. In the present study, a delta parallel mechanism system with three degrees of freedom was developed that saves and reproduces skilled hand motions in three dimensional work spaces. An external sensor that measures the distance between the object and robot is attached to the mechanism and thus guarantees the reproducibility of hand motions against variations in the initial position. The validity of the proposed system was confirmed analytically and experimentally. In the experiment, writing motions by a hard pen were saved and reproduced; the proposed system demonstrated a performance superior to conventional systems.
In this paper, a time-delay compensation method based on work space communication disturbance observer (WCDOB) is proposed. Time delay degrades the stability of a control system. Communication disturbance observer (CDOB) has been proposed to solve this problem. However, CDOB cannot compensate for time delay in multi-degree-of-freedom bilateral control systems with different configurations, because the inertia of the robots is not fixed. In contrast, WCDOB can estimate the time delay based on work space information and compensate for them. The experimental results confirm the validity of the proposed method.
In this study, parameter identification of a spiral motor by finite element analysis (FEA) and experiments was validated using the least-squares method. The parameters were utilized in the controller design to maximize the performance of the spiral motor. The parameters determined from FEA and the experiments were analyzed and compared. The experimentally obtained parameters were very close to the FEA results; thus, the accuracy of the identification was confirmed.
An infant's unhealthy lifestyle increases the risk of adult diseases and the cost of medical care in their future. If the children's life-log is recorded and then their physical condition and transition of activities can be analyzed, it is expected that information can be utilized for the prevention of such issues and for promoting good health. Therefore, activity recognition for infants is discussed in this paper. Feature points are computed from accelerations measured using a 3-axis acceleration sensor attached to the infant's upper-arm, and then, a two-phased classification is performed. In addition, we developed an activity recognition system with database functions and real-time relearning for infants.
This paper presents the use of a water wheel as an alternative to a flow or pressure regulating valve in a water supply system. The proposed system not only controls the flow and pressure but also generates electricity. A sensorless control method is also proposed so that the flow and pressure can be estimated by function approximation of the waterwheel characteristics using the Buckingham π theorem. The performance of the proposed method was validated experimentally.
In this study, a new control method for the power supply of a mass motor is proposed. The reference voltage of the power supply is calculated digitally according to the energy conservation law. Specifically, this method takes into account a servo motor's rotational energy to control the output voltage by inputting an angular velocity to the digital controller. With this method, the voltage ripple of the power supply output is calculated to be reduced by about 40% compared conventional method. This also facilitates the reduction of the output capacitance and peak current and extension of the operating life.
This paper proposes a person search system that uses clothing features. The system uses a camera to obtain the appearance of a person and a range sensor for person detection and direction estimation. The system detects a moving person based on background subtraction using distance information and histogram of oriented gradients (HOG) features. The clothing area is extracted according to the positions of the person's shoulders and waist. The clothes are characterized by four features that are calculated from the color histogram, color differences, frequency, and co-occurrence matrix. The system recognizes the same clothing based on the degree of similarity, which is obtained by comparing clothing features. However, two problems can be assumed: (1) the clothing appearance differs depending on the body direction and (2) the clothing color changes depending on the illumination. For the former problem, we prepared three databases (front/side/rear views) corresponding to the person direction. The system estimates the direction of the person by using information of the body arc based on ellipse fitting. The direction is determined as perpendicular to the long axis of the ellipse fitted to the cross-section of body. Concerning the latter problem, we calibrated the color information to correspond to the environment. The method recognizes clothes by selecting the database provided for the direction of the person; the results showed that it was robust at identifying specific persons.
This paper presents a new motor with three three-dimensional magnetic cores and two loop windings driven by a normal three-phase inverter. This configuration reduces the number of parts, simplifies the production process, and downsizes the motor by a high copper slot fill factor and no end winding. This paper describes the working principle, the design approach, and the prototype evaluation results of the motor.
Contactless power transfer systems for charging electric vehicles require a high efficiency, a large air gap, and a good tolerance to lateral misalignment and need to be compact and lightweight. Contactless power transformers have two types of structures: a single-sided transformer with a circular core and a double-sided transformer with a rectangular core. Past studies showed that H-shaped rectangular core transformers are more suitable for vehicles than circular core transformers. However, the cooling of cores located between two magnetic poles is a major challenge for double-sided transformers. In particular, this problem is serious for large capacity transformers such as fast chargers because the loss density is higher than for normal charge transformers. If the radiator interrupts the magnetic flux, not only are eddy current losses created but a coupling is also prevented. This paper proposes a novel cooling structure based on H-shaped core transformers. In the novel structure, radiator metal bars are inserted parallel to the main magnetic flux. As a result, the cooling performance is improved without compromising efficiency.