Patent Publication Number: US-2012038202-A1

Title: Method for Controlling the Depth of Shears

Description:
The present invention relates to a method for controlling the cutting depth of the drums of shearers, also known as disc shearer loaders, used as recovery equipment in underground coal mining, according to which the cut of the drums into the country wall or rock is detected by means of measured values and the cutting depth of the drums is adjusted by control signals derived from the measured values. 
     Such a method is known from DE 31 27 702 A1. Here, the solid-borne noise that is induced by the cutting forces brought about at the respective drum by the material being engaged is measured by a solid-borne noise detector mounted on the supporting arm of the drum. The oscillation amplitudes of the solid-borne noise are evaluated and are compared, for adjustment purposes, with the frequency spectra characteristic on the one hand for the cutting of coal, and on the other hand for the cutting of country rock. From this comparison, control signals are generated for adjusting the cutting depth of the drums. Unfortunately, a drawback of this method is that it does not operate with the necessary precision, since the transmission of the solid-borne noise data via the supporting arms of the drums is subject to further influences, such as bearing rigidity, vibrations that occur, and the like. 
    
    
     It is therefore an object of the present invention to provide a method of the aforementioned general type that operates with an improved precision. 
     The realization of this object, including advantageous embodiments and further developments of the invention, results from the content of the patent claims, which follow this description. 
     The basic concept of the invention is that during the recovery or shearing operation, the current consumption (I SM ) of the cutting motors, which drive the drums, and the traveling speed of the shearer (V M ), are detected as measured values, from which the respective specific cutting energy (E SP ) is determined or measured in a computer as the ratio of the current consumption (I SM ) to the traveling speed (V M ), whereby a respective characteristic value for the specific cutting energy (E SP ) is determined for different mining conditions in accordance with the resistance or compactness of the coal that is to be recovered and of an outcrop of the country wall or rock, whereupon when this value is exceeded, a cut of the drum into the country wall or rock is assumed, and corresponding control signals are generated for correcting the cutting depth of the drum. 
     In this connection, the invention utilizes the expended specific cutting energy (E sp ) of shearers as the criterium for recognizing differences in the minerals cut by the drums that are characterized by different hardnesses. The specific cutting energy (E SP ) results from the following mathematical interrelationship: 
     
       
      
       E 
       SP 
       =P 
       SM 
       ×η/V 
       M 
       ×D 
       w 
       ×T 
       w 
      
     
     where
         P SM =Cutting motor power   η=Output   V M =Speed of the Machine   D w =Drum Diameter   T w =Drum Cutting Depth       

     Since the values for D w , T w  and η can be applicable as constant values, and the power P SM  of the pertaining cutting motor can be assumed to be proportional to the cutting motor current, it can thus be applicable that the specific cutting energy (E SP ) corresponds to the ratio of cutting motor current (I SM ) to the traveling speed (V M ) of the shearer. 
     The specific cutting energy differs depending upon whether the drum cuts in the coal or in the country rock. As a function of specific deposit or seam conditions, characteristic values can be set for the specific cutting energy for different coal layers, as well as for country rock of differing formation, and hence for individual mining operations. To this extent, the characteristic values are set as parameters in the computer. 
     As the recovery operation continues to run, the respective specific cutting energy that is to be expended is determined in the computer, and is compared for adjustment purposes with the characteristic values that are stored in the computer. In this way, it is possible to determine whether the drum is cutting in the coal or in the country rock, and also whether portions of the country rock are being cut along. From this comparison, corresponding control signals can be generated for correcting the cutting depth of the drum, and in conformity therewith the cutting depth of the drum can be corrected. 
     In this regard, the present invention has the advantage that an automatic recognition of the boundary layer between coal and country rock, or an automatic tracking of the boundary layer during the cutting operation, can be achieved, and in particular not only for the leading drum in its contact with the roof of the seam, but also for the trailing drum in its contact with the footwall. 
     In particular in order to avoid imprecise measurements during the start-up of the shearer, it is provided pursuant to one exemplary embodiment of the invention that the calculation of the specific cutting energy (E SP ) in the computer be carried out only above a traveling speed (V M ) that is established as a lower limit, which, for example, can be assumed at 3 dm/min. 
     The features of the subject matter of these documents disclosed in the preceding description, the patent claims and the abstract, can be important individually as well as in any desired combination with one another for realizing the various embodiments of the invention.