Conveyors: power-driven – Conveyor section – Endless conveyor
Reexamination Certificate
2002-05-21
2004-04-06
Ellis, Christopher P. (Department: 3651)
Conveyors: power-driven
Conveyor section
Endless conveyor
C198S834000, C198S718000, C198S719000
Reexamination Certificate
active
06715601
ABSTRACT:
The present invention relates to a method for the control of the chain drive mechanisms of underground working machines, especially chain scraper conveyors, as well as a corresponding chain scraper conveyor.
DE 43 16 798 A1, to whose published content reference is made here, proposes a generic underground chain drive mechanism, which is provided with a multiple disc clutch with hydraulic closing pressure adjustment and a measuring and control device, in order to satisfy the different requirements on modern drive systems with continuously rising installed performance, high reliability and high endurance of all components with a compact construction of the drive system. The drive mechanism for the chain operation of the underground working machine, especially of a face conveyor, comprises two drives, of which one forms the main drive and the other an auxiliary drive and each has a mains fed electrical drive motor, whose drive revolutions and motor torque which can be transmitted to a chain wheel via a two stage gearbox unit, of which at least the second is constructed as a planet drive. The core of each drive unit is a multiple disc clutch, which is assigned to the hollow wheel of the planet drive and detects and adjusts to the various operating conditions and functions, such as smooth starting, overload protection, load equalisation, creeping travel and high starting torque can be controlled. The multiple disc clutch comprises here a fixed clutch packet and a movable clutch packet joined to the hollow wheel, which are pressed together with the coupling pressure prescribed by the control, by means of a hydraulic cylinder controlled by a servo valve. By using a controlled retardation of the hollow wheel, its revolutions and, thereby, the slippage can be adjusted to any desired value between 0 and the maximum revolutions of the hollow wheel. For the control and the regulation of the drive, its operating data are continuously captured, the measured values are evaluated in the evaluation device and regulating values are output from a regulating circuit to the controller of the closing pressure adjustment. The multiple disc clutch is a wet running multiple disc coupling with special clutch linings, so that the power transmission is practically wear-free. The heat arising from slippage between the clutch packets is removed via heat exchangers and a cooling water circuit. The chain wheels of the main drive unit and the auxiliary drive unit drive the circulating chain together, which in face conveyors comprises horizontal and vertical chain elements as well as the scrapers.
In face conveyors with comparatively short chain lengths, i.e. a distance of up to some 350 m, the measuring and evaluation unit, together with the load equalisation, slippage control and overload protection, assures secure operation of the chain scraper conveyor, mostly without failures. With increasing chain lengths, especially in chain scraper conveyors with long chains, i.e. a distance between main and auxiliary drive units of more than 400 m, the problem of chain breakage in the bottom strand, i.e. the empty run of the chain, increases disproportionately. The applicant for the present application has conducted intensive research, to determine the cause of these chain breaks, so that constructional and/or control engineering measures to avoid chain breakages can be undertaken. The latest results from experimental measurements have shown that a chain break in the bottom run often precedes an upwards turning curve of the chain force, so that the cause of the chain break could lie in vibration phenomena of the chain. In this it was shown relatively quickly that transverse vibrations of the chain cold be eliminated as the cause of high dynamic chain forces, so that the investigations were broadened into longitudinal power swings.
Chain breakage in the bottom run presents a real problem, so that it is a main aim of the invention to ameliorate this problem. An attachment to avoid longitudinal swings in the chain by mechanical means, which increase the damping in the chain system, had to be abandoned because of too great a liability to wear, high cost and the greater need for maintenance within the permanently changing chain loading. The applicant of the present application has therefore gone over to reproduce a chain scraper conveyor, together with its drive arrangements and the chain in a model and to research in the model the causes for the vibration phenomena and to simulate measures for their removal.
The main result from this model building and simulation is that vibration phenomena, which finally lead to overloading such as chain breakage or to a shaft break, can be traced back to characteristic chain vibration effects. The chain vibrations depend here strongly on the friction of the chain in the top run and in the bottom run, including the specific characteristics of the friction curve. In the top run a damping is effected by the loading of the pans between the scrapers, which works against the occurrence of characteristic vibrations. In the bottom run on the other hand a substantially greater dependency of the characteristic vibrations on the friction curve is evident, since the characteristic curve of the friction of the chain has a negative gradient and the coefficient of friction reduces with increasing running speed of the chain.
Accordingly taking account of the results discussed above the invention is directed to a method for the control of vibration phenomena in chain driven underground working machines such as conveyor installations or mining extraction machines in which by means of a detection device a detection signal, representative of the current vibration arising in the chain, is filtered out from the operating data of the main and auxiliary drives and taken to an active suppressor, which in dependency on the detection signal, generates a time-variable signal in accordance with a suppression function, with which, in the frequency range of the vibration of the chain, a change is effected in the control value for the closing pressure setting of the multiple disc clutch of at least one, preferably both drive units by the abstraction of energy or the introduction of energy in the chain. For the first time a method is proposed with the present invention, in which information on the current state of vibration in the chain is obtained by means of a detection device and from this using an active suppressor a control signal is generated as a phase shifted exciter, which changes in the same frequency range as the vibration of the chain and by superimposition on the vibration leads to its damping or suppression. The method according to the invention can cost effectively be connected into the presently available regulating structure, integrated in the measuring and control device, since by means of the control signal a change is effected in one of the controlling values in the control structure. Chain drive arrangements with multiple disc clutches with closing pressure adjustment offer here the special advantage that a direct access to the process is possible by their construction and control structure. In drive units with multiple disc clutches it is actually possible to obtain a rapid change in the revolutions of the chain wheel by suitable reduction of the oil pressure in the closing pressure adjuster of the multiple disc clutch. By changing the closing pressure the slippage between the plates is caused to increase, and consequently the hollow wheel accelerates and the drive revolutions of the drive and the chain wheel are reduced. Conversely by increasing the closing pressure the hollow wheel can again be retarded and the chain wheel accelerated. These changes of the control value for the closing pressure setting can be carried out within the frequency range, which is necessary for the active suppression of the vibration. The preferred area of use of the method according to the invention is the suppression of the natural vibrations of the chain; since the method can be used for all the vibration phenomena
Abel Dirk
Breimhorst Arno
Haese Erwin
Herkenrath Peter
Kostiza Nicole
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
DBT Automation GmbH
Ellis Christopher P.
Sharma Rashmi
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