A pneumatic actuator has several advantages such as low heat generation, a high power-to-weight ratio, and low costs; however, it also has disadvantages such as time delays, nonlinearities, and position-dependent multiple pressure resonances. In this study, we propose a wave equation-based model, which can fit the position-dependent pressure resonances based on delay elements, taking into account the damping. Using this model, a wave cancellation filter is proposed for canceling all the resonances and anti-resonances. The effectiveness of both the model and the filter were verified through experiments.
In order to realize force sensorless fine force control, this paper proposes a new notch-type friction-free disturbance observer (DOB) and a new notch-type friction-free reaction force observer (FFRFO). Generally, a force sensorless force control system is always influenced by the static friction phenomenon. In order to suppress the estimation error due to static friction, a force sensorless force control system uses a dither signal, and a friction free reaction force observer (FFRFO) is used to consider this dither signal. Since the high frequency gain charactheristics of conventional FFRFO are significantly higher than 0dB, the entire force control system sometimes becomes unstable or produces oscillating responses. To overcome this problem, this paper proposes a new force sensorless control system using the notch-type friction free reaction force observer, whose inner system is the proposed acceleration control based on the notch-type friction free disturbance observer. The effectiveness of the proposed system is confirmed by experiments using an actual industrial robot.
Manufacturing equipment and scientific instruments, including wafer scanners, printers, microscopes, and medical imaging scanners, require accurate and fast motions. An increase in such requirements necessitates enhanced control performance. The aim of this paper is to identify several challenges for advanced motion control originating from these increasing accuracy, speed, and cost requirements. For instance, flexible mechanics must be explicitly addressed through overactuation, oversensing, inferential control, and position-dependent control. This in turn requires suitable models of appropriate complexity. One of the main advantages of such motion systems is the fact that experimenting and collecting large amounts of accurate data is inexpensive, paving the way for identifying and learning of models and controllers from experimental data. Several ongoing developments are outlined that constitute part of an overall framework for control, identification, and learning of complex motion systems. In turn, this may pave the way for new mechatronic design principles, leading to fast lightweight machines where spatio-temporal flexible mechanics are explicitly compensated through advanced motion control.
This paper examines the response dispersion in the micrometer-stroke point-to-point positioning motion of high-precision servo systems with nonlinear friction, and presents an advanced model-based feedforward (FF) friction compensation technique to improve the servo performance. In servo mechanisms with rolling ball bearings and/or guides, rolling friction is well-known to deteriorate not only the transient response but also the settling accuracy, because of the nonlinear and complicated friction properties in the micro-displacement region. Therefore, effects of the rolling friction on the performance deterioration should be carefully considered to perform precise simulation analyses and to design effective controllers. In this study, first, the mechanism of response dispersion in the micrometer-stroke motion is analyzed in detail through numerical simulations using a rolling friction model. Then, an advanced FF friction compensation technique using the rolling friction model is adopted with consideration of the mechanism of response dispersion. The effectiveness of the rolling friction model-based analyses and the friction compensation are demonstrated for a laboratory prototype linear motor-driven table system.
This paper aims to realize position and torque sensorless motion transmission between a generator and a motor. The proposed voltage compensation method requires only one current sensor on the generator side. Since the motor side is completely sensorless, this system is suitable for operation under harsh environments. Comparative analyses indicate that the proposed method satisfies the conditions for the transmission of an actual tactile sensation. Simulations and experiments confirmed that motion transmission is realized using the proposed method.
An aging society is a serious problem in many developed countries. Due to this issue, there has been a significant increase in the demand for assist devices that can support human motion. This paper proposes a novel assist device, Intelligent Tension Pole (ITP), to assist in indoor activities of daily living (ADL), and it is expected to provide support for achieving self-reliance, space saving, and stability. The structure and control system of this assist device are presented. This novel assist device is based on a movable handrail, and therefore wheels are added to the lower and upper ends of the tension pole. In addition, a ball screw, which enables the ITP to move while stretching to the floor and ceiling at any time using force control, is added. In order to improve user comfort and reduce the risk of falling down of the ITP, translation and inclination controls of the ITP are applied to the wheel control. These controls are controlled independently by the mode decoupling method. Experiments are conducted to verify the effectiveness of the proposed device and its control system.
A dual active bridge (DAB) dc-dc converter is suitable for bidirectional high-power transfer. However, it has a limited soft-switching range and a high peak current during low power transfer with traditional phase-shift modulation (PSM) when there is a variation in the input/output voltage. To overcome solve this difficulty, this paper proposes a new modulation strategy, combined pulse-width modulation (CPWM) which combines single pulse-width modulation (SPWM) and dual pulse-width modulation (DPWM), with a unified fundamental phase φf for a wide power transfer range. Unlike previous modulation strategies, CPWM is applicable for bidirectional power transfer. In order to combine SPWM and DPWM, this study comprehensively analyzes the soft-switching range and the peak current of PSM, SPWM, and DPWM. The CPWM strategy is experimentally tested using a 1.6kW prototype to verify the improvement in efficiency and its bidirectional power transfer capability. The experimental results show efficiencies of both positive and negative power transfers were improved by using CPWM.
Linear resonant actuators (LRAs) have been used in a wide range of applications because they utilize mechanical resonance and operate at high efficiency. However, the amplitude of LRAs severely decreases when external load is applied. To solve this problem, we applied PID (Proportional-Integral-Derivative) control to an LRA, and the mover amplitude remained constant against an external load. When a large external load was applied with the target voltage of PID control high, however, input power reached maximum and the amplitude did not follow the target value. As a solution, it is effective to utilize electrical resonance and generate large current. In this paper, we propose a control method to generate an electrical resonance. The effectiveness of the proposed method was verified through dynamic characteristic analysis employing two-dimensional finite element method and measurements.
Previously, the authors had proposed an indoor positioning system based on multiple frequencies of ultrasonic waves. This system had a systematic positioning error caused by the attenuation of both ultrasonic waves in air and signals in the detection circuit. This study proposes an error correction method based on an attenuation model, along with directivity models of ultrasonic waves. According to our evaluation, the average error in positioning was reduced to 2.52cm, which is 18% smaller than the simple correction obtained in the previous study. The additional calculation time required for the proposed model was 0.7-3.8ms on Arduino Uno. This is an extended version of a work presented at an IEEJ technical meeting in March 2017.
Optimal allocation of wireless power transfer system (WPTSys) for electric vehicles (EVs) plays an important role in reducing the manufacturing costs of WPTSys. In the conventional approach, the allocation of WPTSys requires information on EV operation such as speed profile and power demand. This paper proposes a new methodology based on mathematical optimization for the simultaneous design of EV speed profile and allocation of WPTSys in a lane segment, with the aim of reducing the cost of WPTSys by minimizing its length. By parameterizing both EV operation and allocation of WPTSys as unknown parameters, an optimization problem with constraints of EV operation and battery sustainability is established for optimizing these unknown parameters to minimize the length of WPTSys. Therefore, the optimal speed profile of EV and optimal allocation of WPTSys can be simultaneously determined. The proposed approach is applied to a scenario of autonomous driving EVs, where it is assumed that the designed speed profile is accurately tracked. A numerical case study is conducted to illustrate the proposed approach. Furthermore, it is shown that our proposed method achieves WPT systems that are shorter in length compared to those obtained using the conventional method under the same operational constraints of EV and battery.