Power plants – Pressure fluid source and motor – Having means controlling or attenuating shock vibration,...
Patent
1997-08-08
1999-01-12
Nguyen, Hoang
Power plants
Pressure fluid source and motor
Having means controlling or attenuating shock vibration,...
91361, F16D 3102, F15B 1316
Patent
active
058573330
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Hydraulic piston cylinder assemblies are often equipped with a closed loop system controlling the position, the pressure, the force or the speed of the unit. Accordingly the piston stroke for example is determined by a distance transducer and this actual quantity as measured and a desired value are delivered to an electronic controller generating an error signal from both quantities and generating therefrom a positioning variable for controlling a valve controlling the fluid path between the power unit, a fluid pressure source and a reservoir.
The quality of the control system can be improved by feeding back certain output variables in a closed loop.
For example, output variables such as the speed and the acceleration of the power unit are fed back for improving a position control.
The output variables are sensed or, respectively are calculated in using a model generator. Due to the quality of the distance signals a differentiation does usually not result in any improvement.
In piston cylinder assemblies having one-sided or two-sided piston rods the differential pressure in both cylinder chambers can be used for an output variable control.
However, certain operative conditions of hydraulic power units cannot be appropriately controlled by merely sensing the distance, the speed, the acceleration or sensing the differential pressure. In the return stroke of a large press, for example, the open valve for decompressing and returning the fluid displaced from the cylinder space to the reservoir may cause severe vibrations, in particular in elongate pipe lines or, respectively in large fluid volumina which vibrations cannot be counterarted by any known speed or acceleration feedback means since the output variables required are scarcely to be measured. This is particularly true for the output variable control of low frequency hydraulic power units including plunger cylinders which are not equipped with an appropriate distance sensing system. A further application is noise reduction of hydraulic power units, for example in stamping and nibbling machines. Here the noise primarily is generated the tool breaks through the material. Breaking through under load results in a high acceleration of the piston resulting in loud noise.
SUMMARY OF THE INVENTION
An object of the invention is to provide a control system for dampening low frequency hydraulic power units and/or dampening vibrations occurring in voluminous spaces or voluminous pipelines, in particular for dampening the cutting noise of high frequency power units.
According to the invention, the output variable to be required for the dampening operation is sensed by measuring the hydraulic pressure and the pressure signal is differentiated to generate a pressure signal variation. This pressure variation signal is directly proportional to the variation of the acceleration. According to the invention it is thus not intended to deduce the acceleration variation from the conventional position control or a model. Rather the output variable p i.e. the pressure variation which is proportional to a variation of the acceleration is determined and this very signal is used for controlling the valve. Determining and processing the pressure gradient can be easily conducted in both analog and digital electronic controllers. The pressure can be measured very simply.
The sensed pressure signal can be differentiated one or more times. A single differentiating step is always possible according to experience, whereas a multiple differentiating operation means that rather small disturbance variables will be amplified to an extent such that further utilizing the signal may result in problems. It is thus preferred to generate multiple differentiation signals in a mathematical model to which the pressure signal sensed is delivered and which model resembles the control characteristics of the power unit as is known. Accordingly the differentiation step becomes independent of the disturbance variables as referred to above.
For example, the present invention m
REFERENCES:
patent: 4336745 (1982-06-01), Lund
patent: 4712470 (1987-12-01), Schmitz
patent: 5140895 (1992-08-01), Imanishi
patent: 5230272 (1993-07-01), Schmitz
Patent Abstracts or Japan vol. 16, No. 36 (M-1205), 31 Oct. 1991 & JP,A,03 244804 (Daikin Ind Ltd) 31 Oct. 1991.
Neumann Joachim
Reinert Michael
Schmidt Stefan
Mannesmann Rexroth GmbH
Nguyen Hoang
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