Abstract:
The invention relates to a control device for an extracting unit in the face of a mine, for actuating the hydraulic actuator in the sense of drawing, stepping, setting, and having a plurality of main valves for connecting the actuator of the extracting unit to a main pressure line and a main return line, and a similar plurality of pilot valves, each associated with a main valve for adjusting same and connected to the main pressure line via a pilot pressure line common to all pilot valves and connected to the main return line via a return line common to the main valves and the pilot valves. The pilot pressure line can be shut off and the return line can be blocked off from the main return line and connected to a measuring device for measuring escaping hydraulic fluid.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a control device for an extracting unit in the face of a mine. 
     2. Description of Related Art 
     A control of this type is generally known. 
     However, the prior art suffers from the problem that the main valves and the pilot valves can be subject to inner leakage; in particular, in the presence of high pressures of 450 bars that occur. Due to the high energies of leakage flows, they cause damage to the main valves and/or pilot valves rendering them inoperable; in addition, a drop of hydraulically supported loads results. 
     Consequently, attempts are being made for detecting leaks early. However, this is a difficult feat in cases of inner leaks between main pressure and/or main return lines and return pressure and/or return lines. Attempts to detect such leaks by means of sound measurements have been unsuccessful to date, because it is not possible to distinguish permissible noises, in particular flow noises, from impermissible flow noises. 
     Therefore, it is the object of the present invention to be able to detect leaks at any time involving only minimal complexity in terms of devices and labor, even in existing systems while said systems are in operation. 
     SUMMARY OF VARIOUS EMBODIMENTS 
     The solution according to one embodiment is based on the realization that, although the main pressure of the face is applied to pilot and main valves from a joint main pressure line, the indicated device-related steps, as specified according to some embodiments as well as the method steps according to other embodiments allow, all the same, for differentiated leak detection on main and pilot valves. 
     The type of measuring instrument that is employed for measuring escaping hydraulic fluid is for the most part optional. The significant aspect of any selection provides that pressures of 300 bars and higher can be accommodated, and that, at very low pressure and flow rate, at least a qualitative measurement should be possible. 
     The improvement according to some embodiments allows for an automated leak measurement without the need for a further switching step, as soon as the main and pilot valves are in an operating state in which the connection to the return is shut off. To this end, the recoil spring of the check valve is adjusted in such a way that there is a correlation of the pressures, which are necessary, on the one hand for the operation of the measuring instrument and, on the other hand, on the inside of the return line for opening the check valve as well as for connecting the return line ( 9 ) to the main return line ( 5 ). 
     In the improvement according to one embodiment, a branch-off is provided upstream of the check valve, which is available as a standard solution, for the discharge of leaked fluid to the measuring instrument. While the check valve opens and closes the return line in relation to the main return line automatically and pressure-dependently, a closure can be provided for the discharge of leaked fluid to the measuring instrument ( 20 ) in order to accommodate the operational special aspects of the measuring instrument. 
     The improvement according to another embodiment has the advantage that the measuring instrument remains in operation during all operational states of the control. The output signal of the measuring instrument is continuously detected; however, it is only evaluated as a leakage measurement in such operational states when the return line is not actuated by the pilot and main valves and is, therefore, switched pressure-less, meaning it should be closed by the check valve. This allows for a continuous recording of leakage measurements. It is thus possible to detect if the leakage unexpectedly increases thus pointing to the presence of a defect, or if the leakage exceeds a preset limit value requiring service and repair work on the system. 
     Automation is achieved in that the check valve closes the connection of the main return line to the bypass, and which check valve is shut off in the direction of flow from the bypass to the main return line ( 5 ) by a recoil spring that is considerably weaker than the recoil spring of the check valve in the return line. It is thus achieved that the bypass in relation to the main return line is open even at low pressures in the presence of which the return line to the main return line and the tank is still shut off. 
     Due to the fact that the flow volume meter is disposed in a bypass of the return line ( 9 ) with connection to the main return line ( 5 ), it must be able to withstand very large flow volumes, and/or it must be effectively protected against great and, in particular, flow volume pulses while, on the other hand, it is automatically actuated with sufficient precision, when the system is at a standstill. This protection is provided by the improvement as set forth in another embodiment. 
     Many model types of flow volume meters are commercially available and with a variety of principles of action. Some embodiments reflect the essential principles of action. Static, meaning volumetric flow volume meters, are also expedient for detecting the smallest leaks. Hydrodynamic flow volume meters with pressure measuring instrument require a flow rate; however, on the other hand, they are robust and not vulnerable even when exposed to pressure pulses. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The drawing explains the invention using embodiments.  FIG. 1 ,  FIG. 1A  and  FIG. 2  show control means of an extracting unit in the work face of a mine for actuating the hydraulic force-transmission device  1  (shown as a cylinder/piston unit) in the sense of a drawing, stepping and setting of the extracting unit, also referred to as the powered support assembly. The following description applies for all embodiments, unless specific reference is made to a single embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Each power-transmission device can be connected by means of lines  2  and  3  with the main pressure line  4  and the main return line  5 . The main pressure line and the main return line extend through the entire the work face, meaning all extracting units are connected thereto in the shown manner. Each power-transmission device has an associated main valve  6  that controls the connection of the lines  2  and  3  to the main pressure line and the main return line. To this end, all main valves  6  are connected via pressure line  8  to the main pressure line  4  and via return line  9  to the main return line  5 . 
     For their actuation, the main valves  6  are hydraulically pilot-controlled by pilot valves  7 . To this end, the pilot valves are actuated by magnets, not shown here, of the electronic input means  10  in such a way that the main valves are actuated by means of the hydraulic control lines  11 , 12  in the one or the other sense. For this purpose, the pilot valves are also connected to the main pressure line  4  and the main return line  5 ; specifically, to the main pressure line  4  via the line path from pressure line  8  and pilot pressure line  13 , and to the main return line  5  via the line path from return line  9  and pilot return line  14 . Using the pilot valves, the necessary pressure for adjusting and holding the pressure in the main valves is adjusted in lines  11  and  12 . 
     Furthermore, the hydraulic system is provided with check valves and filters that do not require any further description in the present context. 
     A filter  17  is mounted in the pilot pressure line  13  that is common to all pilot valves. Said filter can be exchanged with a barrier that is presently additionally depicted as shut-off valve  18 . 
     Regarding  FIG. 1 : 
     A branch-off valve is installed in the return line  9  that is common to all valves, meaning main and pilot valves, that shuts off the connection to the main return line  5  and by means of which the return line can be connected to a measuring instrument  20 . 
     However, the return line can also be shut off solely by means of the check valve  21  alone, which must always be present to prevent that any pressure that may become built up in the main return line from reaching the return line  9 . Said check valves  21  is preloaded by a recoil spring  24 , for example, having a spring force corresponding to 2 bars. The branch-off valve  19  is replaced by a T-piece  22  in the return line  9 , having the branch-off for the discharge of leakage to the measuring instrument  20  serving for measuring the leak. 
     This can be seen in the detail view as depicted in  FIG. 1A . Since this leakage discharge is pressure-less, the closing force of the recoil spring  24  in check valve  21  is sufficient for closing the connection between the return line  9  and the main return line  5 . Thus, the leak cannot flow back into the main return line  5 ; instead, it cannot help but reach the measuring instrument  20 . A shut-off valve  28  can be provided in the branch-off for deactivating the leak-measuring action. 
     The measuring instrument can be, for example, a measuring vessel that collects the volume of the leaked hydraulic fluid occurring over a given time unit, and by which it can be measured. 
     Preferably, all of the valves and lines shown herein, including filters, check valves, etc. of a powered supply assembly or of a group of force-transmission devices of the powered support assembly are housed and arranged inside a steel block. This has, until now, impeded the detection of leaks on the inside of such a steel block because said steel block is connected to the main pressure line pressure, (e.g.) 450 bars, as well as the main pressure return line pressure, (e.g.) 30 bars, which is why leaks do not escape to the outside. 
     However, by means of the additional equipment according to the invention, it is possible to detect if inner leaks of impermissible size are present and, if so, in what amount said leaks must be associated with leakage at the location of the pilot or main valves. 
     To this end, first, by actuating the shut-off valve  18  or exchange of the filter  17 , the pilot pressure line  13  is shut off by means of a (not shown) shut-off element. The branch-off valve  19  is then readjusted in order to shut off the connection of the return line  9  to the main return line  5 , establishing instead the connection to the measuring instrument  20 . The leakage during a given time unit provides the first measured value. The pilot pressure line is now reopened and the leak is measured once more for the given time unit as a second measured value. The first measured value represents any leakage solely of the main valves; the second measured value represents the inner leak for the entire system. The difference between the first and second measured values represents the leakage for the pilot values. If one of these values and/or the difference exceeds a preset limit, the system is deactivated until the leak has been repaired by a replacement of the affected valve elements. 
     Regarding  FIG. 2 : 
     A T-shaped branch-off  19  is mounted in the return line  9  that is common to all valves, meaning main and pilot valves, to which a bypass  27  with connection to the main return line  5  is connected. Bypass  27  circumvents the check valve  21 . A flow volume meter is disposed in the bypass as a measuring instrument  20 , as well as a second check valve  25 . Said check valve  25  has the same flow direction as the check valve  21  and prevents pressure that can build up in the main return line from reaching the bypass  27 . Said check valve  25 , however, is considerably weaker by means of the recoil spring  26 , which is, for example, the preload is less than 1 bar, than the check valve  21 , on the other hand, which has a recoil spring  24  having, for example, a preload of 2 bars. A damper is disposed upstream of the flow volume meter as a flow resistance  23 . This way, it is possible to limit the flow volume of the bypass as well as the pressure upstream of the flow volume meter to such a measure as is allowable for the flow volume meter and tolerable as volume loss for the pilot control. Instead of or in addition to the damper, bypass  27  can be equipped with a shut-off valve  28  that is only opened for leakage measurements, see  FIG. 1A . 
     Moreover, using the equipment according to  FIG. 2 , once again, not only is it possible to detect if inner leaks are present and, if so, whether of impermissible volume or not, but also if and at what level these leaks must be associated to pilot or main valves. It is to be noted that the control device  10  detects the output signal of the flow volume meter  20  as a continuous electronic signal via a line that is presently not shown. However, the control device also detects the operating state of the pilot and main control valves. The control device is thus able to detect as to whether an operating state of the pilot and main control valves is actuated for which the return flow line should not have a return flow to the tank. The control device is able to evaluate the output signal of the flow volume meter  20  that is incoming with these operating states as a signal indicating a leak. By actuating the shut-off valve  18  (or replacement of the filter  17  by a (presently not shown) shut-off element), the pilot pressure line  13  can be shut off. Pressure is thus not applied to the pilot valves, and the same are in their resting position. The return line  9  by itself is able to accommodate leakage flow of the main control valves. Said leakage flow generates only minimal pressure that is insufficient for opening the check valve  21  against the spring force  24 ; however, it is sufficient for opening the check valve  25  in the bypass  27  against the spring force  26 . The connection of the return line  9  to the main return line  5  is thus created by means of the measuring instrument/flow volume meter  20 . The leakage of the main control valves can thereby be detected over a given time unit. The shut-off valve  18  of the pilot pressure line can also be opened. The leakage volume that is collected during the same time unit originates from the total system of the pilot and main control valves. The difference of the first and second measured values represents the leakage only for the pilot valves. If one of these measured values and/or the difference exceeds a preset limit, the control device  10  brings the total system to a standstill so that the leak can be repaired, for example by replacement of the affected valve elements.