Agitating – Having specified feed means – Adjustable mixing ratio control
Reexamination Certificate
2000-07-07
2001-11-13
Cooley, Charles E. (Department: 1723)
Agitating
Having specified feed means
Adjustable mixing ratio control
C366S162300, C222S134000
Reexamination Certificate
active
06315442
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for the synchronous conveying of flowable materials. The invention relates furthermore to a device for implementing such a process. More specifically, the invention relates to a process for the synchronous conveying of flowable materials with conveyor pumps in a mixing device, from which the mixture of these materials can be fed to a consumer, for example a spray-paint pistol, whereby the conveyor pumps are each operated by means of a hydraulic adjusting unit, in which one operating piston is guided in an operating cylinder, and whereby the adjusting units lie in a hydraulic circuit of a drive fluid loading the operating pistons. The invention relates furthermore to a device for implementing such a process.
BACKGROUND OF THE INVENTION
A process of this type and an associated device are already known from the Patent Application EP 0 644 025 A1, in which two dosing conveyor pumps convey the individual materials into one single mixing device in such a manner that a drive member of a first conveyor pump is loaded with a constant flow pressure and the flow pressure of the drive fluid loading a second drive member are each controlled by adjusting commands of a control device such that the through-flow measured values of the conveyor streams fed by the conveyor pumps have a predetermined relationship, which can be superimposed onto the control device as a desired value.
During a relatively slow conveying of the materials such a control indeed assures their homogeneous mixing. It is possible, at relatively high conveying speeds, for inhomogeneities to occur in the conveyed mixed goods, which can cause difficulties during technical use.
Moreover, the operating efficiency of the control depends essentially on the pressure measurements and controls in the circuit of the drive fluid, which demand measuring devices for the occurring pressures. The demand measuring devices can be calibrated and operate reliably over long periods of time. The measured values from these pressure measurements must thereby be connected with measured values for the travel paths covered by the operating pistons, for the determination of which distance sensors are mounted on the operating cylinders, which are controlled by the operating pistons themselves or by back and forth moving structural parts connected to these. The measured values of pressure and travel distance must then in addition be mathematically connected in order to obtain therefrom the actual values for the conveyor streams out of the conveyor pumps and, therefrom the actual mixture ratio of the materials fed to the mixer. Time delays must be expected in particular for mechanical measurement of the pressures. It is therefore not certain that the materials are continuously processed into a homogeneous mixture, which at all times has the desired mixture ratio. Rather local heterogeneities and deviations from the mixture ratio can, at times, not be avoided in the finished mixture.
It is also already known to carry out the conveying of the materials by means of conveyor pumps, each single one of which is driven by a hydraulic adjusting unit, and in which the flow of the drive fluid active in the adjusting unit can each be adapted by a control valve, which is controlled by a proportional governor. Even though high conveying pressures and performances can be easily handled here, the arrangement often cannot accomplish a mixing of homogeneous goods, which mixing is constant in a wide conveying range, because the adjusting units cannot be synchronized with one another in such a manner that the conveying directions correspond always in various adjusting units, especially when a reversal in direction of the operating piston movement takes place at the same time.
Therefore one obvious solution already used is to enable the drive of several adjusting units to be carried out only by one single drive unit so that the conveyor pumps are now operated simultaneously and one indeed achieves a homogeneous distribution of the conveyed materials in the mixed goods. The condition for a satisfactory operation is hereby a fixed and unchangeable mixture ratio. However, if one wants to change the mixture ratio, the conveyor pumps must be changed. In addition, adjustable gearing does not help when the technical parameters are supposed to be maintained very precisely without earlier additional expensive tests being carried out on the system.
Such a gearing is also called a swivel arm, with which at times a kinematic connection between the operating pistons is created, and which can be adjusted in such a manner that the ratio of the operating strokes carried out with the operating pistons can be changed. The maximum operating stroke of one of the adjusting units is mostly left constant and the operating stroke of the second adjusting unit is changed. The system must also be newly adjusted after each change. More difficult yet is that only limited drive and conveying performances can be realized with such lever gearings. The adjustment is connected with a considerable time input.
EP Patent 0 116 879 B1 discloses a process including an associated device, in which, in place of the pressure measured values, the through-flow measured values of the conveyor streams are measured and are superimposed as counting impulses onto a control device, and the conveyor volume of the participating materials are thereby determined in such a manner that in a first mixer, the mixing block, a desired mixture ratio is approached. The finished mixture is partially transported into a second mixer, the mixing pipe, from which it then can be continuously removed by a consumer. Thus at least two mixers are needed in order to create a continuously conveyed mixture.
The basic purpose of the invention is therefore to design a process and an associated device of the type identified in detail in the beginning in such a manner that a continuous mixing of the materials in one single mixing chamber and in one specified mixture ratio to one another occurs, the size of which moves in an interval, which meets all demands. Homogeneous throughout mixed goods are thereby obtained. A simple, robust and inexpensive device is able to be operated with an inexpensive control.
The purpose is attained, according to the invention, by a process wherein the control of the mixture ratios is very much simplified because now merely the operating strokes must be measured in the adjusting units. The ratio is characterized by a constant operating stroke of a first adjusting unit and an operating stroke of the second and each further adjusting unit, which operating stroke can be changed and defines the mixture ratio. Since the movements of the operating pistons occur simultaneously, and merely the flow of the operating fluid is controlled by the second and each further adjusting unit, the speed of the operating pistons change in the following adjusting units. Successful distance sensors are available for length measurement of the operating strokes, which sensors are already being used in such processes.
To carry out the process of the invention, a device can be used having at least two. Two adjusting units which are designed as double-acting hydraulic cylinders and are hydraulically connected with one another in such a manner that the drive fluid conveyed under the influence of the drive motor out of the first adjusting unit drives the second adjusting unit in the same direction. Thus, the first adjusting unit functions hereby as the drive of both a first conveyor pump for a first material and also as the drive of a second adjusting unit and thus of a second conveyor pump associated with same for a further material without the adjusting units having been mechanically connected with one another. The above-described disadvantages of such a connection are avoided here. Also a separate drive for each of the conveyor pumps is not needed in the case of the device of the invention. Its adjusting units are separately hydraulically coupled with one another, and care must merely be take
Cooley Charles E.
Flynn, Theil, Boutell & Tanis, P.C.
WiWa Wilhelm Wagner GmbH & Co. KG
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