A 3‐DOF Inchworm Using Levitation Caused by Vertical Vibration

We propose a 3‐DOF inchworm‐type microactuator that uses levitation generated by vertical vibration. The vertical vibration is created by a piezoelectric actuator. The inchworm typically consists of thrust elements and clamp elements. The proposed inchworm, however, does not use any clamp elements. Four levitation elements are connected with four thrust elements, which are stacked‐type piezoelectric actuators. The levitation element consists of a mass, a piezoelectric actuator, and a plate. The vertical vibration of the piezoelectric actuator lifts the levitation elements, which eliminates any friction. By controlling the order of the deformation of the horizontal piezoelectric actuators and the vibration of the vertical piezoelectric actuators, the inchworm engages in linear and rotational motion. The levitation height and the linear and rotational displacement of the inchworm were measured. Experimental results demonstrated the feasibility of the proposed 3‐DOF inchworm. The mechanism described in this paper is effective for a precision positioning system in a clean room.     

Hanging‐type mag‐lev system with permanent magnet motion control

A type of mag‐lev system with permanent magnet motion control is proposed, analyzed, and examined experimentally. In this mag‐lev system, the levitating object hangs on the upper iron rail and such parts as magnets, sensors, and actuators are installed on the object. This levitation method is very useful for noncontact conveyance systems, because the conveyance path is very easy to make. This paper describes the success of the construction of the hanging‐type magnetic levitation system using magnet motion control mechanism. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 63–70, 2000     

A small‐size self‐propelled Stewart platform

This paper describes a self‐propelled Stewart platform. The Stewart platform usually consists of a base platform, a moving platform, and linear actuators connecting the platforms. We use six stacked‐type piezoelectric actuators as linear actuators. Mechanical joints connected the linear actuators and both of the platforms. We inserted electromagnets between the linear actuators and the base platform instead of the mechanical joints. This structure enables the Stewart platform to move on a surface by using the principle of inchworm motion. While the electromagnets fix the linear actuators on the base platform, the proposed Stewart platform realizes a precise 6‐DOF motion. Control signals are designed for small displacement based on inverse kinematics, and for a wide working area based on the principle of inchworm motion. The position and orientation of the moving platform are measured, and experimental results indicate the feasibility of the proposed mechanism. The mechanism is effective for a precise position system which has unlimited working space. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(2): 37–46, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21261     

Biomechanical analysis of legrest support of occupied wheelchairs: comparison between a conventional and a compensatory legrest.

This study was undertaken to investigate the effects of elevating legrest on posture and pressure distribution in a group of ten able-bodied subjects sitting in a manual wheelchair. Two types of legrest were tested: a conventional elevating legrest with a fixed axis of rotation, and a compensatory elevating legrest with a moving axis of rotation. A three-dimensional (3-D) kinematics analysis was carried out to assess body posture simultaneously with pressure measurement data collected at the back, seat, calf and foot supports. The compensatory legrest enables to lengthen foot support as the legrest proclines. This compensation at the knee joint level has a beneficial effect in minimizing pelvic and thigh motion as well as in reducing pressure distribution under seat and foot supports. In contrast, the use of a conventional legrest modifies significantly the subject's posture and induces a substantial increase of 40% on pressure data under ischial tuberosities in procline position. These findings are important for disabled and elderly people who need to elevate their lower leg frequently.     

Teaching to Facilitate the Transfer of Learning [Educator's Corner]

An amusing anecdote that is old (having appeared in Esquire and Reader's Digest over half a century ago) concerns a man who experienced severe motion sickness during train travel whenever he would ride backwards, i.e., sat facing the rear of the train; so he learned to exchange such a seat by requesting the passenger sitting opposite to him. When he got off the train very sick and nauseated one day, his friend receiving him at the train station asked what was wrong. He replied that he had been riding the train backwards. "Why didn't you ask the person sitting across from you to change seats with you?" asked his friend. "How could I," said the traveler, "There wasn't anybody in that seat."     

Studies on thrust characteristics of high‐thrust spiral motor

Linear actuators are used in various industrial applications. Conventional linear actuators are a combination of a rotational motor and a ball screw, a hydraulic actuator, or a linear motor. However, these actuators have some demerits. This paper proposes a spiral motor (SPRM) that comprises a helical stator and a helical mover. Owing to its helical structure, the SPRM can be expected to show better performance compared to the conventional linear actuator. A stator and a mover are shown in Figs. 1 and 2, respectively. Helical motion is obtained by this motor and only linear motion is extracted by canceling rotational motion at the end effector. There are two types of SPRMs. One has no ball screw on the output axis, while the other has a ball screw. The former can be used in a direct drive system. However, the gap between the stator and the mover should be controlled because the motor is a magnetic levitation system without a ball screw. Further, the motor requires two three‐phase inverters. The other motor is easy to control because it does not require gap control. However, the motor is inferior to the first motor with regard to position control since the friction in this motor is larger. In this study, a prototype of the SPRM is developed. The prototype constructed is a motor with a ball screw. In this motor, the stator and mover are made of block cells. The stator block is shown in Fig. 3 and the mover block is shown in Fig. 4. The prototype of the SPRM shown in Fig. 5, is developed by using these two blocks. An experiment is conducted to examine the driving of the SPRM. The experimental result is shown in Fig. 6. From this result, it is evident that comprising a helical stator and a helical mover can generate linear motion. Another experiment is conducted for measuring the thrust characteristic of the motor. The result obtained is shown in Fig. 7. From the figure, the thrust constant of the spiral motor, K_f, is obtained as 538.0 N/A. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(2): 58–64, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21168     

Parameter design of event‐driven logic controller for two‐wheeled vehicle

Programmable Logic Controllers (PLCs) are widely used in industry. In PLC‐based control systems, low‐resolution (especially ON‐/OFF) sensors are inexpensive, and actuators are commonly used because they are compatible with programming languages used in PLCs. PLC switches the actuators ON/OFF as the state of the sensor changes between ON/OFF. In designing PLC‐based systems, the design of the parameters of these sensors and actuators (e.g., position of limit switches and torque of motors) is an important problem because they affect the overall performance of the system. This problem, however, has not yet been fully discussed. In the present paper, a systematic design method for this problem is developed. The main concept is to express the model of the system as a Mixed Logical Dynamical System (MLDS) and to formulate the problem as a mathematical programming problem. The developed idea is applied to the line‐following control of a two‐wheeled vehicle. The usefulness of the proposed method is demonstrated through simulation and experiments. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(2): 51–60, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20584     

Model predictive control for tendon‐driven balloon actuator on simulation

Many pneumatic actuators have been developed to be lightweight with high output for decreasing the impact force. However, for pneumatic actuators it is difficult to maintain exact control because these actuators have constraints. In this study, we developed model predictive control (MPC) that can accommodate these constraints when applied to the pneumatic actuator we developed. As described here, we compared and evaluated the control performance using MPC and proportional–integral–derivative (PID) control with an anti‐windup control system. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

行走式尺蠖压电直线驱动器研究现状及关键技术综述

尺蠖压电驱动器具有大行程、高精度、大输出力、快速响应、无磁场影响等优点,在超精密定位领域具有广泛的应用前景。而行走式尺蠖压电驱动器又以箝位机构结构简单、刚度和动态性能好,中间驱动机构偏摆小,整体体积小,运动稳定性好等特性引起世界各国的关注。在阐述行走式尺蠖压电驱动器的本质、组成结构及运动原理的基础上,对其国内外研究现状及其关键技术进行了分析,并对其发展趋势进行了展望。     

The use of selective electrical stimulation of the quadriceps to improve standing function in paraplegia.

Persons with spinal cord injury (SCI) can benefit significantly from functional neuromuscular stimulation (FNS) systems for standing if manual tasks can be performed while upright. Using FNS to sufficiently activate the knee extensors to rise from a sitting position often results in inadvertent activation of the rectus femoris and/or sartorius, which flex the hip. In this study, intramuscular electrodes implanted in the vastus lateralis and medialis of four subjects with SCI were used to activate these muscles individually and simultaneously to measure knee extension moment. Support forces applied to the arms and feet were measured while upright to quantify the effects of recruiting rectus femoris and/or sartorius. In three of the four subjects, vastus lateralis, by itself, generated adequate knee extension moment for rising from a chair and to maintain static standing. Simultaneous activation of the vastus lateralis and medialis using a bifurcated electrode generated adequate knee extension moment in one subject, and was within 10% of the required moment in another. While upright, activation of the rectus femoris resulted in arm support force increases of 4-11% body weight, while deactivation resulted in arm support force decreases of 6-9% body weight. The results indicate that selective activation of the vastus lateralis, individually or in combination with vastus medialis, can improve current FNS standing systems by reducing the arm support forces required to remain upright.     

Dynamic Characteristics Analysis of Two‐DOF Oscillatory Actuator and Experimental Verification of Prototype

Recently, linear oscillatory actuators have been used in a wide range of applications. In particular, small linear oscillatory actuators are expected to be used in haptic devices by being extended to provide multi‐degree‐of‐freedom motion with arbitrary acceleration. In this paper, we propose a compact two‐DOF oscillatory actuator that can move in various directions on a plane. The static and dynamic characteristics of the actuator are determined by the 3D finite element method. The effectiveness of this method is shown through a comparison of the measured results with the experimental results from a prototype. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 58–65, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22312     

Intention detection using a neuro-fuzzy EMG classifier

One of the most important factors in prosthetic and orthotic controllers is the ability to detect the intention of the person to perform a certain activity such as standing up, quiet standing, walking, and sitting down. For these applications, detecting the intention of the person to perform an activity relieves them from the burden of conscious effort in operating the system. Electromyography (EMG) has been used extensively for intention detection and can be considered a bandlimited stochastic process with Gaussian distribution and zero mean, which has varying spectral characteristics in time. Various EMG features have been used for intention detection including the number of zero crossings, the EMG frequency characteristics, and the mean absolute values. There are a number of drawbacks that have been associated with these methods such as the high electrode sensitivity to electrode displacement, low recognition rate, and a perceivable delay in control. In this article we discuss a technique for EMG applications that decreases global delay time and improves time spectral analysis. The technique is aimed at improving the Gabor matching pursuit (GMP) algorithm through the use of genetic algorithms. The key stage of this design feeds EMG features to a neuro-fuzzy classifier that can be designed to detect the intention of the patient.     

LMI‐based adaptive output feedback fault‐tolerant controller design for nonlinear systems

This paper presents 2‐novel linear matrix inequality (LMI)‐based adaptive output feedback fault‐tolerant control strategies for the class of nonlinear Lipschitz systems in the presence of bounded matched or mismatched disturbances and simultaneous occurrence of actuator faults, including failure, loss of effectiveness, and stuck. The constructive algorithms based on LMI with creatively using Lyapunov stability theory and without the need for an explicit information about mode of actuator faults or fault detection and isolation mechanism are developed for online tuning of adaptive and fixed output‐feedback gains to stabilize the closed‐loop control system asymptotically. The proposed controllers guarantee to compensate actuator faults effects and to attenuate disturbance effects. The resulting control methods have simpler structure, as compared with most existing recent methods and more suitable for practical systems. The merits of the proposed fault‐tolerant control scheme have been verified by the simulation on nonlinear Boeing 747 lateral motion dynamic model subjected to actuator faults.     

Analysis of postural perturbation responses

People with cerebellar ataxia lack lower limb coordination and dissipate sway motion slowly and inefficiently after a posture perturbation. We report a practical and low-cost “human resonance frequency test” for both laboratory and clinical use to quantify progress in balance and cerebellar rehabilitation. We assumed that the center-of-pressure (COP) oscillation rate of decay following a standing posture perturbation is directly related to resonance frequency; a more rapidly dissipating COP oscillation about the position of equilibrium indicates, by definition, more efficient postural control. We hypothesized that following successful physical rehabilitation, people with cerebellar degeneration will have a faster rate of decay of the COP response to an external perturbation. Because the COP is modulated by a synergy of trunk and lower limb motion strategies, COP decay rate may be a useful measure of lower limb coordination in people with cerebellar ataxia. The method was applied to three subjects with cerebellar ataxia before and after rehabilitation; there was good agreement between the calculated COP decay rate and conventionally used gait stability parameters providing pilot data for this simple approach     

Ultrasonic motors: Their models, drives, controls and applications

In the last decades piezoelectrically driven ultrasonic motors have become alternative actuators to the conventional electromagnetic motors especially for precise and accurate servo positioning applications. Different types of ultrasonic motors have been constructed and manufactured. Several drive systems have been designed, implemented and proposed for these motors. A variety of control techniques have been applied to them. The research given in this study covers bases of the ultrasonic motors. Theoretical background, modeling, drive systems, control techniques and applications of the ultrasonic motors have been introduced. Firstly, the general overview has been given. Then, modeling studies focused on performance estimation and analysis of ultrasonic motors have been examined. Afterwards, drive systems and control techniques of ultrasonic motors have been investigated. Furthermore, an example drive and control system has been presented. This drive system has been designed as to be controlled digitally. In addition, the important industrial and research applications of these motors have been included. The presented study has been arranged as a review of ultrasonic motors. The important points of specifications, models, drive systems and control methods of the ultrasonic motors have been emphasized.     

Whole-body vibration during manual wheelchair propulsion with selected seat cushions and back supports

Although the exposure to whole-body vibrations (WBV) has been shown to be detrimental to seated humans, the effects of wheelchairs and seating systems on the transmission of vibration to an individual have not been thoroughly examined. The purpose of this study was to determine if the selected wheelchair seat cushions and back supports minimize the transmission of vibrations. Thirty-two wheelchair users traversed an activities of daily living course three times using 16 randomly selected seating systems as well as their own. Vibrations were measured using triaxial accelerometers at the seat and participant's head. The weighted fore-to-aft (T/sub x/), vertical (T/sub z/), and resultant (T/sub r/) transmissibility based on the vibrational-dose-value (VDV) were used to determine if differences existed among the four seat cushions and back supports. The obstacles that seem to have the largest effect on the transmission of WBV are the single event shocks and the repeated event shocks. Comparisons between the individuals own seating system and the tested seating systems suggest that the individuals are not using the most appropriate seating system in terms of the reduction of vibration transmission.     

Dynamic modeling and adaptive robust boundary control of a flexible robotic arm with 2‐dimensional rigid body rotation

This paper investigates the control of a single‐link flexible robot manipulator with a tip payload appointed to rotate about 2 perpendicular axes in space. The control objective is to regulate the rigid body rotation of the manipulator with guaranteeing the stability of its vibration in the presence of exogenous disturbances. To achieve this, a Lyapunov‐based control design procedure is used and accomplished in some steps. First, the partial differential equation (PDE) dynamic model governing the rigid‐flexible hybrid motion of the arm is derived by applying Hamilton's principle. Next, based on the developed PDE model, an adaptive robust boundary control is established using the Lyapunov redesign approach. To this end, an adaptation mechanism is proposed so that the robust boundary control gains are dynamically updated online and there is no need for prior knowledge of disturbance upper bounds. The actuators and sensors are fully implemented at the arm boundary without using distributed actuators or sensors. Furthermore, in order to avoid control errors resulting from the spillover, control design is directly based on infinite‐dimensional PDE model without resorting to model truncation. Simulation results illustrate the efficacy of the considered method.     

Novel Piezoelectric-Based Power Supply for Driving Piezoelectric Actuators Designed for Active Vibration Damping Applications

This paper describes a novel step-up DC-AC piezoelectric-based power supply for driving piezoelectric actuators. Piezoelectric actuators have been demonstrated to be very attractive in applications requiring fast response and high actuation force, such as active damping applications. These actuators are commonly installed in self-powered systems (cars, helicopters, aircrafts, satellites, etc.) with limitation in the battery performance, dimensions and maximum weight. Nevertheless, the required driving electrical AC voltage for these actuators is typically in the range of 100 V to 1000 V, quite far from the 9 to 24 V of common batteries. Thus, the use of heavy, large and EMI-noisy electromagnetic transformers becomes necessary which is a drawback for the compact size required. This paper introduces an alternative system for driving piezoelectric actuators using a novel design of piezoelectric transformer, the Transoner®. The proposed solution allows a reduction in size, weight and magnetic noise generation compared to the classical electromagnetic-based systems. The work represents a completely novel approach to the possibilities of piezoelectric transformers for powering high voltage piezoelectric actuators. The solution offers significant advantages in environments requiring high integration, low weight, and low electromagnetic interferences operated with batteries. A circuit configuration capable of converting a 24 V DC input voltage up to 600 V _pp AC output voltage with frequency and magnitude control is implemented. Experimental results are presented for a standard multilayer piezoelectric actuator driven at 100 V _pp within the range of 10 Hz to 500 Hz.     

A multidomain model of planar electro-active polymer actuators

Dielectric electro-active polymers (EAPs) have a significant deformation response to electrical stimulation. The ease of fabrication of these materials makes them very suitable for product-integrated actuators. Existing electromechanical models do not fully integrate all aspects of the physical behavior needed to design such actuator systems. This paper presents a fully integrated, multidomain model for such EAP actuators, combining the electrostatic properties of the electrical circuit with the compliant electrodes, the actual force output in the translation direction, nonlinear elastic behavior, and damping of the polymer material. The capabilities of the developed model are discussed and verified with laboratory experiments.     

Active fault‐tolerant control system design with trajectory re‐planning against actuator faults and saturation: Application to a quadrotor unmanned aerial vehicle

During the past 30 years, various fault‐tolerant control (FTC) methods have been developed to address actuator or component faults for various systems with or without tracking control objectives. However, very few FTC strategies establish a relation between the post‐fault reference trajectory to track and the remaining resources in the system after fault occurrence. This is an open problem that is not well considered in the literature. The main contribution of this paper is in the design of a reconfigurable FTC and trajectory planning scheme with emphasis on online decision making using differential flatness. In the fault‐free case and on the basis of the available actuator resources, the reference trajectories are synthesized so as to drive the system as fast as possible to its desired setpoint without violating system constraints. In the fault case, the proposed active FTC system (AFTCS) consists in synthesizing a reconfigurable feedback control along with a modified reference trajectories once an actuator fault has been diagnosed by a fault detection and diagnosis scheme, which uses a parameter‐estimation‐based unscented Kalman filter. Benefited with the integration of trajectory re‐planning using the flatness concept and the compensation‐based reconfigurable controller, both faults and saturation in actuators can be handled effectively with the proposed AFTCS design. Advantages and limitations of the proposed AFTCS are illustrated using an experimental quadrotor unmanned aerial vehicle testbed.Copyright © 2013 John Wiley & Sons, Ltd.