Hydraulic Actuation System Research Articles

Differential PWM Control of Hydraulic Actuator System with Locking Mechanism.

In the preceding papers, the authors proposed a method of the differential PWM for a hydraulic actuator operated by two 3-way high-speed solenoid valves. The actuator operated by this method shows good linear characteristics as a controller which achieves accurate positioning. However, when the actuator is connected to a load with large force over Coulomb friction, an oscillatory motion appears in the steady state. Therefore, the actuator control system becomes considerably inaccurate. To solve this problem, a new type of actuator, which has 4 check valves, is designed in this study. The dynamic characteristics of the actuator, which has a spring as a load, are investigated by simulations and experiments. Consequently, it is clarified that the actuator can be controlled with high accuracy, retaining a merit of the differential PWM method, and moreover, that the permanence of the proposed actuator can be improved by adopting a locking mechanism.

Digital control of hydraulic actuator system operated by differential pulse width modulation.

This study deals with an electrohydraulic servo system which is operated by two 3-way high-speed solenoid valves in the PWM digital mode. It has often been pointed out that there are practical problems to be solved in the conventional PWM systems, such as serious nonlinearities in the valve characteristics. In order to overcome such problems, a new concept of PWM control, that is, a differential PWM method, is proposed in this study. The strategy of this method is to eliminate/minimize significant nonlinearities, such as the dead zone, which regularly appear with conventional methods. In the new method, the pressure difference for driving the actuator is given by pulse trains, their widths modulated by duty input to the valves. The dynamic characteristics of the system driven by the propoded method are investigated by experiment and digital simulation. Consequently, the availability of the proposed method is confirmed well.

Digital control of hydraulic actuator system by the method of differential-pulse width modulation.

This study deals with a hydraulic actuator system operated by two 3-way solenoid valves in PWM-Digital mode. It has been often pointed out that there are practical problems to be solved in the PWM system. For example, (1) Accuracy of positioning control becomes considerably insufficient, because the system is affected by on/off action of the solenoid valves, and (2) Serious nonlinearity appears in the valve characteristics as a result of the switching behavior of the valves. As a method to overcome these defects, a new concept of PWM control, that is, a differential PWM method, is proposed in this study. In the method, the pressure difference for driving the actuator is method, is proposed in this study. In the method, the pressure difference for driving the actuator is given by pulse trains which are modulated by Duty-input to the valves. The dynamic characteristics of the system, controlled by the proposed method, are investigated by experiment and digital simulation. Consequently, the availability of the proposed method is confirmed.

Measurements of the oscillatory lateral derivatives of a high incidence research model (HIRM 1) at speeds up to M = 0.8

SummaryTests were made to investigate the effects of Mach number on the oscillatory lateral derivatives of a three-surface, high-incidence research model (HIRM 1). Effects of Reynolds number and frequency parameter were also investigated at low speed. A new flexible sting and hydraulic actuator system were designed for the tests in the 2.4 m x 2.4 m Pressurised Wind Tunnel.Results showed that the effects of Reynolds number and frequency parameter were not very significant at low speeds but there were quite large effects of Mach number on some derivatives, notably yawing and rolling moments due to sideslip and rate of yaw.

２方向型電磁弁による油圧アクチュエータのＰＷＭディジタル制御

This study deals with a hydraulic actuator system which is operated by two 2-way solenoid valves in the PWM-Digital mode. The solenoid valves act as converters of electronic-pulse signals to hydraulic-ones.It is considered that the dynamic characteristics of the system depend largely on the be h avior of on/off action of the solenoid valves. The response performance of the system, for example, might be inevitably affected by the time lag existing between the input and output signals of the valves. Details of such effects of the solenoid valves, however, have yet to be satisfactorily clarified, mainly because an adequate mathematical model for the system has not been developed. The object of this study is, therefore, to prop o se a mathematical model for the PWM-actuator system. The dynamic charateristics of the system are investigated by the method of digital simulation based on the proposed model. The simulated time responses are compared with the measured ones to confirm the validity of the mathematical model.

Static test of an ultralight airplane

This paper describes all of the work necessary to perform the static test of an ultralight airplane. A steel reaction gantry was designed first, then all of the loading whiffletrees, the hydraulic actuation system, and instrumentation systems were designed. Loads and stress analyses were performed on the airplane and the gantry and whiffletrees. Components tested to date are: tubing samples, cables, and two-by-four whiffletrees. A hydraulic system consisting of a 3000-psi hand pump, 10,000-pound actuator, pressure gage and lines, and a Barksdale valve are described. Load cell calibration and pressure indicator calibration procedures are also described. A description of the strain and deflection measurement system is included. Preliminary data obtained to date are compared to the analytical predictions.

健常人と同等の階段降り歩行が可能な大腿義足

This paper deals with an attempt to develop an above-knee prosthesis which allows amputees smooth stair descending and level walking at a voluntary walking pace. First, the dynamic analysis of normal persons' level walking and stair descent/ascent were carried out to obtain general prospects for the design and the control of an A/K prosthesis. The summary of the analyses is as follows. (1) The active planter-flexion moment (more than 100Nm) must be effected at an ankle joint on a stance phase during stair-ascending. (2) The passive extension moment (max 80Nm) must be effected at a knee joint on a stance phase during stair descending. (3) A little active extension moment is necessary at an ankle joint on a swing phase for rapid walking to walk on a flat surface and also to ascend stairs. (4) A passive flexion moment must be effected at an ankle joint through a swing phase during stair descending; however a little extension moment (about 3Nm) is necessary at termination of a swing phase to sustain some extension angle. One hydraulic actuation system was then proposed on the basis of the analytical results, which allows amputees to descend stairs smoothly as well as to walk on a flat surface with no external power source. The proposed system was assembled into the A/K prosthesis WLP-7. Amputees wearing WLP-7 can walk on a flat surface at a voluntary walking pace and also can descend stairs as well as normal persons after only half an hour of training.

UCL Hydraulic Arm Dynamics

The UCL arm prosthesis is briefly described and its general performance capabilities outlined. Evaluation tests were conducted to assess the dynamic response of the hydraulic servo actuator systems. These included measurements of saturation velocity and stall load of the main arm articulations. Detailed observations were made of the shoulder elevation function, the heaviest loaded actuator, to provide data on the transient response of this servosystem. An analysis is described of a general hydraulic actuator used as an angular position controller, and this is simplified and used as the basis of a digital simulation of the shoulder motion. Results of running the digital simulation show a very good correlation with the experimentally derived data. The paper concludes by re-emphasizing the considerable advantages to be gained by using hydraulic actuation, illustrated by these test results.

Chamber Bleed Auxiliary Power Unit

The use of gases bled from a propulsion unit as an energy source for auxiliary power units (APU's) has been investigated and shown to offer significant weight and envelope savings in comparison with conventional warm gas generators. The principal challenge associated with this use of chamber-bled gases lies in conditioning the hot, particle-laden gases to a state compatible with the energy transfer device (e.g., turbine, air motor). Filter designs which remove 100% of the metallic particles in the exhaust gas and which have efficiently reduced chamber gas temperature by thermal decomposition of a sacrificial material have been demonstrated. Four candidate coolant materials have been characterized by subscale testing. Heat transfer models have been formulated which adequately predict the performance of coolant bed designs. Two full-scale demonstration tests of a combined filter-cooler have been conducted. Approximately 8 hp was delivered to a hydraulic actuation system for the 21.4and 40.3-sec test durations.