Kazuo Nakano

Comparative Study on Dynamic Characteristics of Hydraulic, Pneumatic and Electric Motors

Hydraulic or pneumatic motors are replacing electromagnetic servomotors in many applications. It is important for engineers and designers to select adequate actuators in given servo applications. In a previous paper, Nakano had predicted the performance of future electric or hydraulic motors after that there have been many advances in actuators. In this paper the performance of hydraulic and pneumatic motors, and electric AC servo and DC motors has been calculated, surveyed, and evaluated on the basis of specifications listed for them in current catalogs and nonpublic data. We selected 765 different kinds of electric motors and 404 different kinds of fluid power motors available in the market. Power density, torque–inertia ratio, power rate, and power rate density were selected as the performance indexes for comparison. Rated power and torque were found to be nearly proportional to motor mass and moment of inertia, respectively. The electromagnetic motors have developed high performance with large rated torque and a smaller moment of inertia. The newly developed small-size hydraulic motor was also included in the performance index, and its characteristics were plotted. The compact size of fluid power actuators has great potential for power rating or quick response.Copyright

Electro-hydraulic servovalve using a PMN multimorph

Abstract Static and dynamic characteristics of the deflection have been investigated on a multimorph bender element made with PMN-based electrostrictive ceramics. Using this multimorph, we have developed a high-speed electro-hydraulic servovalve responsive up to 2 kHz with a bandwidth of more than 1 kHz.

RF signal generator using time domain harmonic suppression technique in 90nm CMOS

This paper proposes an RF signal generator using a time domain harmonic suppression technique based on Fourier series analysis. The circuit consists of four differential ring voltage control oscillators (VCOs) with phase differences and the pulse signal summing circuit. By summing pulse signals from VCOs with appropriate phase differences determined by Fourier series in time domain, the third and fifth harmonics can be cancelled without filters. To confirm the validity, a prototypal RF signal generator was fabricated in 90-nm CMOS technology. As a result, we succeeded in generating an RF signal from digital pulse signals. The frequency range is from 1.1 to 3.7GHz with 1-V power supply. The suppression of both the third and fifth harmonics are below -48dBc at 1.1GHz and -42dBc at 3.7GHz.

An Approach for Remote Measurement of Instantaneous Flowrate by Making Use of Hydraulic Pipeline Dynamics. 3rd Report A Study on the Estimation Errors at the Instantaneous Flowrate Measurement due to Parameter Changes.

We have proposed a remote instantaneous flowrate measurement method, a quasi-remote instantaneous flowrate measurement method and an instantaneous flowrate measurement method by using pressure measurements at two separated points along the pipeline for estimating unsteady flowrate through an arbitrary cross section of the pipeline in hydraulic control systems. In these approaches, unsteady flowrate can be accurately estimated by using the distributed parameter models of the hydraulic pipeline with considering unsteady velocity distribution over the cross section of the pipeline. Under unsteady laminar oil flow conditions, the excellent agreement of estimated and measured flowrate waveforms by a cylindrical choke type instantaneous flowmeter is obtained.Because these approaches make use of the distributed parameter models for estimating unsteady flowrate, the spatial resolution along the axial direction of the pipeline has an outstanding ability. The accuracy and dynamic response of the estimated unsteady flowrate depend on the values of the parameters used such as the length of the pipeline, kinematic viscosity of the oil, sonic velocity inside the oil-filled pipeline, radius of the pipeline; therefore, it is possible that such variations would cause the estimation errors of unsteady flowrate measurement due to parameter changes accompanied by varying an operating conditions.The paper describes the estimation errors of unsteady flowrate measurement due to parameter changes in quasi-remote instantaneous flowrate measurement method and instantaneous flowrate measurement method using pressure measurements at two separated points along the pipeline. By introducing error performance index, the influence of parameter changes on the accuracy and dynamic response of the estimated unsteady flowrate are evaluated. Of the four parameters, the variations of the length of the pipeline and sonic velocity produce large errors in the estimated unsteady flowrate during transient periods. The kinematic viscosity is relatively insensitive in the estimated unsteady flowrate.

Energy-saving hydraulic power source with inverter-motor drive. (Pressure estimation using state variables of electric motor).

Advances in power electronics and microprocessors have provided new opportunities in the application of inverter-motor drive systems. The speed control of AC induction motors can be realized easily by use of an inverter-motor drive at a low cost, high efficiency and wide speed range. From the viewpoint of saving energy, the authors have proposed and developed a new type of variable delivery hydraulic power source with an inverter-motor drive. In this power source, the speed of the fixed displacement pump is controlled by the inverter motor so as to deliver the necessary minimum flow rate for the duty cycles of the servo system.In this system, the system pressure and pump delivery flow rate are estimated indirectly by the state variables of the inverter motor. The principle of the pressure estimation is experimentally confirmed. The programmed control system and digital feedback control system using an estimated system pressure are developed. It is demonstrated that both systems are able to control the hydraulic power source according to the duty cycles of the servo system.

A Simple Method of Selecting Parameters of the Air Chamber to Suppress Oil Hammer in the Pipeline with Constant Upstream Pressure

Valvesw hich are connectedt o long pipelines in a large hydraulic system are occasionally closed very rapidly owing to unavoidable circumstances. The instantaneous stoppage of the flow in the pipeline causes the oil hammer phenomenon resulting in pressure rise which must be properly suppressed from the viewpoint of safety of the pipeline system.In this research, suppression of the oil hammer due to the instantaneous valve closure at the downstream end of the hydraulic line is considered and for this purpose the accumulator and its entrance choke are installed at the upstream side of the valve. The suppressing method are analyzed experimentally and theoretically to get the optimum value of the parameters of the accumulator and its choke. The simples traightforward procedure to determine the optimum parameters are established and its effectiveness are confirmed by the additional experiment.