Digital Actuator Research Articles

マイクロパラレルマニピュレータのディジタル駆動系の研究(S49-1 パラレルメカニズムとその応用(1),S49 パラレルメカニズムとその応用)

In order to develop high precision micro parallel manipulators, a concept of micro parallel manipulators with digital actuation system has been proposed. The digital actuation system is composed of a series of bi-stable-pair mechanisms with simple actuators. Because each bi-stable-pair mechanism with a simple actuator has only two states with high repeatability, sensors for feedback of actuators are not needed for positioning tasks of micro parallel manipulators with digital actuation system. A composition of bi-stable-pair mechanism for wide-range of stroke requirements has been proposed. Some experimental results with macro-size bi-stable-pair mechanisms have been also shown and discussed.

ELECTRIC FIELD INDUCED ANTIFERROELECTRIC TO FERROELECTRIC PHASE TRANSITION OF Pb (Zr,Sn,Ti)O3 CERAMICS AND TAILORING OF PROPERTIES THROUGH COMPOSITION MODIFICATION

In order to obtain a new kind of antiferroelectric (AFEt) ceramics wi th lower AFEt-Ferroelectric (FER) switching field Ef and less hysterisis loss ΔE for application of large displacement actuato r, Ba2+ ionics was employed to control the relative stability between AFEt, FER, and parroelelctrics (PEc) phases in (Pb097-xBaxLa002)(Zr055Sn035Ti01)O3 (0≤x≤02) system. Structural chan ges and electric properties as a function of Barium content x have been investig ated by X-Ray diffraction, dielectric properties, polarization and longitudinal strain measurement. It is observed that AFEt changes to FER, and finally to ferroelectric relaxors(RFE) as Ba content x increases from zer o to 02. Based upon these expermental result, we are able to tailor the AFE-FE switching parameters such as Ef, ΔE and AFEt operating t emperature range ΔT through modifying the Ti/Sn ratio near AFEt/FER phase boundary in the (Pb087Ba01La00 2)(Zr06TiySn04-y)O3 (004 ≤y≤009) system. Finally, a new kind of AFEt ceramics with Ef =16kV/mm，ΔE=085kK/mm， and longitudinal strain x=01%—02% which is appropriate for application of digital actuators has been obtained. Phase dia gram with composition located near AFEt/FER boundary of t he studied system has been determined.

Antiferroelectric thin and thick films for high-strain microactuators

Niobium-doped or lanthanum-doped lead zirconate titanate stannate antiferroelectric thin and thick films have been prepared on platinum-buffered silicon substrates by a modified sol-gel method and their electric properties were characterized, with emphasis on the field-induced phase transition strains. All the films demonstrate zero remanent polarization and a maximum polarization of more than 30 μC/cm2. By choosing the appropriate compositions, the films can have either “square” hysteresis loops with very sharp phase transition or “slanted” hysteresis loops with gradual phase transition. The strain levels of the thin films can reach 0.32% with smaller hysteresis or 0.42% with moderate hysteresis. The thick films can either have a strain level of 0.38% with very small hysteresis or have a strain level of 0.48% with clear digital actuator response. Hence the strain levels of these antiferroelectric films are comparable to that of bulk materials and double that of PZT ferroelectric films, and they are very promising for actuation applications in microelectromechanical systems.

Multilayered digital actuator composed of electrostrictive ceramics

In order to depress the hysteresis phenomenon of a digital actuator which is coded with driven numbers of piezoelectric ceramics, a new actuator composed of electrostrictive ceramics of PMW-PNN-PT family has been investigated. The experimental results have indicated that the actuator works well from the viewpoint of the hysteresis property but showed degraded temperature characteristics. Therefore, a new method to compensate the characteristics has further been investigated by combining two ceramics of different temperature coefficient and found that the average temperature coefficient of displacement in the temperature range from 15 to 30°C has been reduced from 1.13 to 0.26%/°C or less. The observed temperature dependence of displacements is in essential agreement with the simulated curve which takes account of the effect of spontaneous polarization of the electrostrictive ceramics.

DIGITALLY CONTROLLED FLOW METERING UNIT WITH DOUBLE ACTUATION FOR FAST TRANSIENT RESPONSE IN AUTOMOTIVE APPLICATIONS

This paper proposes a novel compact, inexpensive, yet versatile flow metering unit which consists of two hydraulic valves incorporated in a single barrel and operated directly by two digital actuators. For the evaluation of the concept, the mathematical model of the unit is developed and validated. The model is subsequently used to investigate the operability and performance of the system. A specific control strategy taking advantage of the system hardware is implemented. The enhancement of the transient response, as compared to single actuation conventional units, is demonstrated. Furthermore, the back-up functionality in case of failure of one of the valves is ascertained. This kind of double actuator unit is proposed for, but not limited to, fuel metering in a gasoline engine throttle body injection system.

An approach to enlarging the maximum bit in piezoelectric digital actuator

A digital actuator arrangement coded with driven numbers of piezoelectric ceramic pieces has been developed to improve nonlinear response, and hysteresis characteristics as well, in a multilayer piezoelectric ceramic actuator, and adopt it as a displacement device in precise mechanical systems. The proposed 8 bit actuator consists of two sets of conventional 4 bit units driven by different voltages. The experimental results indicate that the actuator works well, showing smooth and linear response.

Powered Orthosis for Lower Limbs -Its Structure and Control-

This paper describes a powered orthosis for lower limbs which restores the gait of locomotion of disabled persons, such as paraplegics, with its structure and control as well as its clinical experiments. The powered orthosis supports the patient's weight, and it has four electrohydraulic digital actuators to motorize hip and knee joints, as well as sensors to detect joint angles and plantar contacts. Each joint angle is controlled by a microcomputer such that an appropriate gait pattern is restored for a stable, powered level walk. This second prototype of the powered orthosis has been designed and developed for testing on patients in order to determine its effectiveness. For the control of this orthosis, the gait pattern is generated by a 16-bit master microcomputer using the preprogrammed pattern which is synthesized with 20 parameters; six 8-bit slave microcomputers measure and control joint angles. A new type of digital actuator was developed specifically for this purpose. In addition, a desktop microcomputer is used for the change of parameters as well as for the dialogue with the master computer. The orthosis weighs only 19.5kg, and the hydraulic power unit 68kg. Clinical experiments of this prototype are conducted on two paraplegics. A powered walk of 6.0 sec/step is realized for the first time, and then 4.5 sec/step for approximately 10 meters.

Powered Orthosis for Lower Limbs and its Clinical Experiments

This paper describes a powered orthosis for lower limbs which restores the gait of locomotion disabled persons such as paraplegics, and its clinical experiments. It supports the patient's weight, has four electrohydraulic digital actuators to motorize hip and knee joints, as well as sensors to detect joint angles, plantar contacts. Each joint angle is controlled by microcomputer in such a way that an appropriated gait pattern is restored for a stable powered level walk. This second prototype of the powered orthosis has been designed and developed to test on patients to see the effectiveness of the powered orthosis. For the control of this orthosis, the gait pattern is generated by a 16-bit master microcomputer using the preprogrammed pattern which is synthesized with 20 parameters; Gsix 8-bit slave microcomputers measure and control joint angles. Further a desktop microcomputer is used for the change of parameters as well as for the dialog with the master computer. The orthosis weighs only 19.5kg, and hydraulic power unit 68kg. Clinical experiments of this prototype have been carried out on two paraplegics. A powered walk of 6.0 sec/step was realized for the first time and then 4.5 sec/step for about 10 meters.

デジタル微分解析器とデジタル制御型機械式加力装置を用いた多自由度振動系のオンライン地震応答載荷実験 : 第2報 多層せん断型架構への拡張

In this paper, the authors have presented a generalized method for solving a non-linear response of multi-degrees of freedom structure based on a newly developted ON-LINE simulation system, which is composed of digital actuators and a digital differential analyzer. In order to examine the efficiency of this system, a series of on-line experiments have been conducted using a two and a three-storied steel building model. The test results have shown that the response obtained by the proposed technique agrees fairly well with a numerical analysis using a simple elasto-plastic hysteretic model.

デジタル微分解析器とデジタルアクチュエータを用いた多自由度振動系のオンライン地震応答載荷実験法 : 第1報 システムの提案

The authors have developed a method of analysis to find the non-linear earthquake response of multi-degrees of freedom structures by using a Digital Differential Analyzer(DDA) and the Digital actuators. Details of the system and the computing method are described herein. Based on this system, the non-linear seismic behavior of the two-degrees of freedom structures subjected to strong earthquakes were experimentally simulated.

New electronically controlled hydrogen-gas injector development and testing

The feasibility of high-pressure hydrogen-gas injection was investigated in a diesel engine with the help of an electronic control under microprocessor management. An injector prototype was developed with variable area orifice fitted with a solenoid actuator for lifting of the needle valve. A metering valve controlled by a digital actuator was installed at the injector's inlet to throttle the gas flow from the cylinder with compressed hydrogen. The injected fuel dose was therefore under double control: by the time of the injector's opening and by the metering valve flow area. This system was first investigated on a test set-up where the pressure in the injector, the needle lift and the gas dose were measured. A concentrated gas discharge rate characteristic of 3 ms duration was obtained. An attempt was also made to measure the gas discharge rate by recording the amplitude of the pressure wave created in a special long pipe. Ignition feasibility tests were finally conducted in a high speed diesel engine with spark ignition support.

Fuel control systems for hydrogen-fueled automotive combustion engines—a prognosis

The state of the art in the field of hydrogen-fueled combustion engines was investigated and conclusions were drawn concerning the future development of fuel control systems for automotive engines using hydrogen as fuel. Assuming the use of modern microprocessor technology together with recently developed linear digital actuators and solenoid operated injectors, basic concepts for fuel control systems were proposed for three mainly used types of combustion engines: gas turbine engine for aircraft propulsion, spark ignition engine for cars and compression ignition engine for vehicles and off-highway equipment. These concepts are based on a liquid hydrogen on-board storage system which seems to be the most feasible for use in the near future.

Closed Loop Step Servo Systems

Stepping motors are motors which receive input in the form of pulses and which move through discrete angular steps in response to them. They also develop a detenting torque which holds the rotor in position after cessation of pulses. On account of these characteristics, stepping motors are found suitable for use as digital actuators in numerical machine tool controls, analog-to-digital converters, etc.Stepping motors can be used in either open loop or closed loop servo systems which are known as step servo systems. The paper describes the design, construction and testing of a closed loop step servo system consisting of the following elements: (i) a bifilar wound permanent magnet stepping motor, (ii) a step discriminator, (iii) memory logic and translator, and (iv) power drivers. The step discriminator is an aluminium disc mounted on the motor shaft and contains 50 holes drilled 7·2° and ¼ in. apart. Four photosensors, spaced 23·4° apart, sense the rotor position and set the levels of four flip-flops accordingly. Logic gates pick off appropriate signals from the flip-flops in accordance with one of the four possible input commands, viz. (1) stop, (ii) high speed, (iii) clockwise, and (iv) counterclockwise, and apply them to power drivers. These, in turn, energize the motor windings. Once an input command is given, the motor pulses itself and keeps on running continuously. The closed loop step servo system can operate either in the single phase mode in which only one motor winding is energized at a time or in the two-phase mode in which two windings are energized simultaneously.Transient response tests on the system show that the motor responds to an input command in one sampling period. Steady state torque versus pluse rate tests show that the motor which could barely run at 150 pulses/sec. with open loop control can run satisfactorily at 500 pulses/sec. in the single phase mode and at 800 pulses/sec. in two-phase mode. Since the motor pulses itself in closed loop control, it does not miss a step even when it runs at 500 and 800 pulses/sec. This is the greatest advantage of closing the digital loop around the stepping motor.