In the field of high precision positioning control, the position servo system must be highly robust against disturbance torque. A Permanent Magnet Synchronous Motor (PMSM) has various torque ripple components that degrade control performance. A portion of the torque ripple is caused by the harmonic current. The torque ripple can be suppressed using a highly robust current control system. The remaining torque ripple is defined as the disturbance torque and is compensated for using a Disturbance OBserver (DOB). However, it is very difficult for a DOB to perform the appropriate compensation because it uses a low-pass filter to reduce noise. To obtain highly robust performance, this paper proposes a new position servo system using a disturbance torque hybrid observer and a current control system in the α-β stationary frame. In addition, this paper uses the torque ripple equation instead of a torque ripple table so as to reduce the amount of Digital Signal Processor (DSP) memory. The effectiveness of the proposed position servo system is confirmed using numerical and experimental results.
This paper proposes a new admittance realization control system based on feedforward compensation for high-stiffness environments. In conventional admittance realization control systems, the poles of the control system can be designed using any design method. However, zeros are placed on the right side of the dominant pole in the pole placement diagram when the environmental stiffness and viscosity values are large. These zeros placed on the right side of the dominant pole deteriorate the frequency response.
In contrast, the proposed admittance realization control system is used to design zeros at the desired frequency. Because the zeros are placed on the left side of the dominant pole, the frequency response of the high-frequency domain is improved. The validity of the proposed method is confirmed by analysis and experiments.
Currently, a high-precision tracking control system is required for a large-capacity optical disc drive system. This paper proposes a new full field-programmable gate array (FPGA) tracking control system based on an error-based communication disturbance observer (ECDOB) considering the time delay of an optical disc drive system. The FPGA control system may have a large influence on both the integer time delay and the non-integer time delay of the control system. In order to consider the time delay, this study reconstructs the feedback control system by using the limited pole placement method. Moreover, this paper proposes a new ECDOB. The experimental and numerical simulation results confirm that the tracking performance of the proposed system is better than that of a conventional feedback control system. In full FPGA tracking control of optical disc systems, the proposed ECDOB-based tracking controller exhibits good performance.
Fast and precise positioning is one of the key requirements for improving the productivity and quality of industrial robots. Many feedforward compensation techniques for 2-degree-of-freedom control systems have already been proposed to realize high-performance positioning. These feedforward compensation techniques can be categorized into two types: 1) point-to-point control and 2) continuous path control. The author has already proposed a deadbeat feedforward compensation technique under the former category, which can ensure the specified settling time for a step reference and can suppress the vibration mode in a mechanical system. In the present study, we enhance the previous method in order to consider continuous path control by applying additional cost functions for gain and phase characteristics.
The effectiveness of the proposed approach is verified using an experimental setup.
Motion control technology is making its way into the unstructured world inhabited by humans. It allows development of applications beyond the structured environment of an industrial plant. Such applications of motion control technology require shifting focus to the models, control strategies and algorithms needed for systems to work, interact, and cooperate with humans or other artifacts in an unstructured environment. Real-world haptic interactions are becoming an important technology with potential application in many different fields like surgery, teleoperation, cooperative work, microsystems, and education. These developments are leading to numerous challenges that need to be solved in order to develop practical and competent systems that support the human operator, and are fault tolerant, safe, easy to use, and capable of adapting to long-term changes in the environment. This paper discusses a number of the emerging issues within motion control technology, including but not limited to new algorithms that allow concurrent force/position control, human-in-the loop control, control in functionally related systems and haptics over internet.
Recently, image sensors for mobile phones have significantly improved, and lens position control is needed for the autofocus actuator of the mobile camera module to realize a robust and precise focus system. The lens position control system is a highly resonant system because the lenses are held by small springs in narrow spaces. In this paper, a digital servo controller for the mobile camera module is discussed. First, continuous control systems are studied for various servo bandwidths with respect to the resonant frequency. Next, three pole assignment methods, 1) multiple poles, 2) a coefficient diagram method, and 3) an optimal controller, are discussed. Third, the limited pole placement method is applied to design a digital controller to suppress the vibration that comes from delay of a system. Finally, a feedforward controller is also investigated to obtain a smooth response for the reference signal. We confirmed that the highly resonant system can be controlled smoothly enough for autofocusing, using the limited pole placement method and the feedforward controller.
A typical electric power-assisted bicycle is equipped with an expensive torque sensor to measure a rider's pedaling torque. In this paper, we propose a method to estimate the pedaling torque from Hall effect sensors mounted on the motor, reducing the cost of electric power-assisted bicycles. It is necessary to separate pedaling torque and load torque from disturbance torque, which is estimated by a disturbance observer. We employ the Fourier series expansion to extract the periodic components of disturbance torque associated with the crank angle, which corresponds to the average pedaling torque. A conditional recursive least squares method is then used to estimate the parameters of the load torque model. Finally, the instantaneous pedaling torque is obtained based on the disturbance observer and the estimated load torque. We confirmed the validity of the proposed method by simulations and experiments. Our method can also be applied to a normal bicycle by replacing its front wheel with a motorized wheel.
Conventional communication-based train control (CBTC) systems enable the frequent operation of trains by detecting train's position and the telecommunication system between the onboard and trackside controllers compared to traditional signalling systems. However, the railway signalling system is still costly, and the cost of the trackside central controllers is particularly high because high-performance failsafe hardware and software are required to control the many pieces of field equipment. Given this situation, we have proposed a concept for a cost-effective CBTC system that provides functionalities equivalent to those of existing signalling systems by using ring topology information shared among the onboard and switch controllers without trackside central controllers. Its basic mechanism is the circulation of a telegram containing information about the exclusive rights to virtual blocks in turn among the controllers within each controlled section. This mechanism reduces the equipment cost to approximately one-third that of a conventional CBTC system. We have now conducted a feasibility study to verify the practicality of this system and have identified potential problems related to system reliability and transportation capacity. This paper presents solutions to these problems and experimental results to show that the proposed system is technically valid and can be applied to many railway lines.
This paper proposes a new modulation strategy for a dual-active-bridge converter. The target of the new strategy is to suppress the circulating current in the converter by minimizing the load angle. The soft-switching operational area is expanded by employing frequency variation together with phase shift modulation. Unlike published modulation methods based on frequency variation, the strategy proposed in this paper can operate under the light or heavy power transmission regardless of the frequency limitation as well as the voltage ratio. As confirmed by experiments, the new strategy can boost the overall efficiency by up to 7% compared to the conventional single-phase-shift method.
In recent years, studies on haptic interfaces have progressed. This study deals with the development of the “Haptic Desk”, which can detect force information and contact position information using a simple mechanism with force sensors. However this technique has low contact point accuracy when the external force is small. Hence, this paper proposes the use of differentiated force information to calculate an accurate contact point. In the experiment, the accuracy of the contact point calculation using the differentiated force information was higher than the one using the force information when the external force was small. Therefore, the error of the contact point decreased regardless of the magnitude of the force when the force information and differentiated force information were used properly.
This paper proposes a novel linear actuator for a tactile display, especially for a Braille interface aimed for the visually impaired, and for a new human haptics interface. The features of such actuators may be evaluated using factors such as output force, stroke, and compactness. The proposed actuator shows better performance in terms of stroke, compactness, and output force compared with existing actuators. The proposed actuator is an electromagnetic linear mini-actuator with two stators and one moving winding. The direction of the output force can be controlled by changing polarity of the input current. The structure of the proposed actuator, simulations, and the experimentally measured data will be presented in this paper.