Patent Publication Number: US-8540176-B2

Title: Crushing plant and method for controlling the same

Description:
RELATED APPLICATION DATA 
     This application is a §371 National Stage Application of PCT International Application No. PCT/SE2008/000306 filed May 5, 2008 and claims priority under 35 U.S.C. §119 and/or §365 to Swedish Application No. 0701459-0, filed Jun. 15, 2007. 
     TECHNICAL FIELD 
     The present invention relates to a crushing plant comprising a crusher, a drive unit which drives the crusher, and a feeding arrangement which feeds raw material to the crusher, the feeding arrangement comprising means for regulating a raw material level in connection with the crusher. 
     BACKGROUND 
     Crushing plants of the above mentioned kind are well known and are used e.g. to refine blast rock into gravel. It is desirable to provide a mobile crushing plant that can easily be moved such that it can be operated at different locations, e.g. at a road construction site. One problem with mobile operation of a crushing plant is that raw material is often fed to the crusher unevenly over time which may cause interruptions in the operation of the crusher. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a crushing plant which is suitable for mobile operation. 
     This object is achieved with a crushing plant as defined in claim  1  or by a method for controlling a crushing plant as defined in claim  10 . 
     More specifically, a crushing plant of the initially mentioned kind then comprises a drive unit being a diesel engine, means for retrieving a parameter value which is correlated to the load of the diesel engine, means for comparing the retrieved value with a threshold value, and means for decreasing the feeding arrangement speed if the retrieved value exceeds the threshold value. 
     By using a diesel engine, the crushing plant may be driven independently of power grid connections. At the same time, it can be avoided to a great extent that the diesel engine stalls due to overload, thereby un-intentionally stopping the crusher. 
     The crushing plant may further comprise means for temporarily stopping the feeding arrangement if the retrieved value exceeds the threshold value. This reduces the risk of stalling of the diesel engine even further. 
     Additionally, the crushing plant may further comprise means for generating a warning if the retrieved value exceeds the threshold value. This informs the users of the crushing plant that the plant operates close to its maximum such that they may reduce the provision of new raw material into the feeding arrangement. 
     The feeding arrangement speed may be reduced by reducing a maximum output from a regulator controlling the feeding arrangement. 
     Alternatively or additionally, the feeding arrangement speed may be reduced by reducing a proportionality constant of a regulator controlling the feeding arrangement. 
     The load parameter value may be retrieved via a J1939 interface. 
     Alternatively, a hydraulic coupling may be arranged on a shaft between the diesel engine and the crusher, the crushing plant comprising means for retrieving first and second speed values relating to the in- and outgoing shafts of the hydraulic coupling, and means for providing the load value based on the difference between the first and second speed values. 
     The crusher may be a gyratory crusher, comprising a hopper mounted in connection with the crusher for providing raw material to the crusher, the raw material level being a level in the hopper, and the feeding arrangement being a conveyor belt. 
     Alternatively, the crusher may be a jaw crusher, comprising a vibration hopper mounted in connection with the crusher for providing raw material to the crusher, the raw material level being a level between the jaws of the crusher, and the feeding arrangement comprising a motor connected to the vibration hopper for providing a vibrating motion. 
     A method for controlling a crushing device of the initially mentioned kind includes retrieving a parameter value which is correlated to the load of the drive unit, wherein the drive unit is a diesel engine, comparing the retrieved value with a threshold value, and decreasing the feeding arrangement speed if the retrieved value exceeds the threshold value. 
     Further objects and features of the present invention will be apparent from the description and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates schematically a crushing plant with a feeding arrangement. 
         FIG. 2  illustrates a control block for the crushing plant of  FIG. 1 . 
         FIGS. 3-5  illustrate different error level to rotation speed control schemes. 
         FIG. 6  illustrates a method for controlling a crushing plant. 
         FIG. 7  illustrates schematically a crushing plant with a jaw crusher. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates schematically a crushing plant with a crusher  1  and a feeding arrangement  3 . In the illustrated case, the crusher  1  is a gyratory crusher with a conical crushing head  5  having an inner shell, and an outer shell  7 , which is illustrated in cross-section. A ring-shaped crushing chamber  9  is formed between the inner and outer shells. The crushing head  5  is connected to a shaft  11  which gyrates under the influence of a drive unit  13  and makes the crushing head  5  carry out a combined rotating and oscillating movement which crushes raw material, typically blast rock, in the crushing chamber  9 . 
     However, the present disclosure is equally relevant also in connection with other types of crushing plants, typically jaw crushers, as will be discussed in connection with  FIG. 7 . 
     A hopper  15 , illustrated in cross-section, is placed on top of the crusher  1  to feed raw material into the latter. The feeding arrangement  3  is adapted for feeding material into the hopper  15  and comprises a conveyor belt  17 , typically driven by a hydraulic motor  19 , although for instance also electric motors are conceivable in this context. 
     It is desirable to accurately regulate the level of the raw material in the hopper  15  and in the crushing chamber, in order to obtain an efficient crushing function. This may be carried out by continuously or repeatedly measuring the raw material level in the hopper  15  and regulating the speed of the conveyor belt  17  accordingly, using a control unit  20 . Measurements may be carried out e.g. by means of one or more ultrasonic sensors, as is well known per se. In the illustrated case, two sensors  21 ,  23  are used that measure the raw material level at two locations of the hopper  15 . This is done to take into account the fact that the raw material level in the hopper  15  will not always be even. Therefore, the average of two or more level sensor signals will provide a more accurate measure of the overall raw material level. 
       FIG. 2  illustrates in more detail the control unit  20  of the crushing plant in  FIG. 1 . First  25 , and second  27  level sensor signals are provided to the control unit  20 , and an averaging function block  29  calculates their average which will be an estimate L act  of the actual raw material level in the hopper  15 . The estimate is compared, using a summer  31 , with a desired raw material level value L req , which may be set by the user. This value may, as is known per se, be chosen to provide efficient crushing with an acceptable quality of the produced gravel with regard to its size distribution, shape, etc. The output of the summer  31  is a level error signal corresponding to L req -L act . The error signal is fed to a regulator  33 , which in the illustrated case is a P-regulator, i.e. produces an output signal P out , which is proportional to the input error signal, at least within a certain range. However, other types of regulators are possible, such as regulators additionally having an integrating and/or a differentiating component (i.e. PD-, PI-, or PID-regulators), or e.g. fuzzy logic regulators. 
     Returning to  FIG. 1 , the output signal of the regulator  33  controls the speed of the feeding arrangement  3 , for instance by controlling a valve of the hydraulic motor  19  which runs the conveyor belt  17 . The control arrangement described so far is capable of regulating the raw material level in the hopper  15  close to a desired level. The control arrangement described herein however has an additional function to improve the overall efficiency of the crushing plant. 
     The drive unit  13  of the crushing plant comprises a diesel engine which drives the crusher shaft  11  via a coupling unit (not shown). The use of a diesel engine makes the crushing plant suitable for a mobile configuration, as a connection to an electric power grid is not needed. The crusher can thus easily be moved from location to location and may therefore be used e.g. in connection with road construction, in order to refine blast rock to gravel. The diesel engine may be controlled, by means of a separate control loop  34 , to run at a predetermined desired rotational speed, e.g. 1500 rpm. 
     A diesel engine functioning as the drive unit  13  may however stall if the power needed to run the crusher becomes too high. This may occur even if the raw material level is regulated to an optimal value, since the density of the material in the hopper  15  may be higher than expected, since the raw material may be harder than expected, or the raw material may be contaminated e.g. with junk or the like. 
     Therefore, a load parameter value P eng  is retrieved from the diesel engine e.g. by means of a sensing line  14  ( FIG. 2 ). The value is correlated to the load of the engine and may be retrieved using the J1939 interface, which is well known per se. Typically the retrieved parameter may be derived from the turbo-charging pressure and indicate a percentage 0-100% of the maximum load. 
     An alternative way of generating a load value is to measure the rotation speed on in- and outgoing shafts of a hydraulic coupling  18 . The rotation speed of the ingoing shaft may be retrieved from a J1939 Interface or may be measured e.g. by means of an inductive sensor. The rotation speed of the outgoing shaft may be measured e.g. by means of an inductive sensor. The load value may be provided based on the difference between the first and second speed values, e.g. by means of a lookup table, and may be provided via a sensing line  16 . 
     The load parameter value is fed to the control unit  20 . The load parameter value may, if it indicates that the engine is close to stalling, affect the control loop of the feeding arrangement such that the feeding of material into the hopper is slowed down. The control unit  20  has a comparator  22  which compares the retrieved load parameter value with a predetermined threshold value, e.g. 80% of the maximum load. If the load parameter value exceeds this threshold, a potential overload condition is indicated. The comparator  22  thus adjusts a parameter of the regulator  33  as will be discussed further. Further, the regulator may be instructed to temporarily stop the feeding arrangement e.g. for a few seconds. 
     Additionally, the control unit  20  may provide a warning by acoustic and/or optic means, typically a summer  35  and/or a flashing lamp  37  (see  FIG. 1 ), if the threshold is exceeded. Alternatively, the warning may be provided before the overload threshold is exceeded by comparing the retrieved parameter with a lower warning threshold (e.g. 70% of the maximum load). 
       FIGS. 3-5  illustrate different error level (input) to rotation speed (output) control schemes.  FIG. 3  illustrates a first case, where a maximum output level is adjusted if a potential overload condition is indicated. The graph  39  thus shows the P-regulator characteristics when no such condition has occurred. The output signal is proportional to the input error signal within a certain range. For even higher error signals, a maximum output level is provided to the conveyor belt motor. Once an overload condition has occurred, the maximum level is lowered as illustrated by the graph  41 , which may e.g. correspond to a 100 rpm lower maximum speed level. Yet another overload condition may make the regulator use a yet lower maximum value as illustrated by the graph  43 . 
       FIG. 4  illustrates a first alternative scheme. In this case, the proportionality constant of the P-regulator is altered by the overload condition occurrence, such that a specific error signal increase results in a comparatively lower output signal increase as illustrated by graphs  39 ′ (no overload condition),  41 ′ (overload condition once), and  43 ′ (overload condition twice). The maximum output is not altered. 
       FIG. 5  illustrates a combination of the two previously described schemes, namely where both the maximum output and the proportionality constant are decreased by an overload condition, as illustrated by graphs  39 ″,  41 ″, and  43 ″. 
       FIG. 6  illustrates a method for controlling a crushing plant. From an initial start-up state  45 , the crushing plant enters an operating state  47  where raw material is refined into gravel. While in the operating state, a load parameter value is retrieved  49  from the diesel engine or from speed monitoring, and is compared  51  with a threshold. If the threshold is exceeded, indicating a potential overload condition, a warning is optionally generated  53 , e.g. as mentioned by flashing a light, and the feeding arrangement is optionally stopped  55  during a predetermined time period. A control parameter in the control loop of the feeding arrangement is then changed  57  to provide a slower feeding, such that stalling of the diesel engine can be avoided. The crushing plant then continues in the operating mode and repeats the measuring procedure within a predetermined time. The speed may thus be decreased further. If the comparing  51  gives the result that the load parameter value is lower than the threshold, the operation of the crushing plant is simply continued. If a parameter has been changed and no new overload condition occurs within a predetermined time, the parameter may be restored back to its previous value. 
       FIG. 7  illustrates schematically a crushing plant with a jaw crusher. The controlling method may be utilized also in connection with such a plant, using any of the control schemes. The jaw crusher comprises a fixed crushing jaw  59  and a swinging crushing jaw  61 , the latter reciprocating against the fixed crushing jaw  59 , due to the rotation of a flywheel  63 , in order to crush raw material between the jaws. A feeding arrangement comprises a vibration feeder/hopper  65 , which is vibrated by means of a vibration motor  67  in order to stimulate the vibration feeder to feed raw material to the crusher. In this case, the vibration motor  67  speed is decreased if the load of the drive unit driving the crusher becomes too high. The raw material level measured may be the level of material in between the crusher jaws. 
     In summary, there is described a crushing plant and a method for controlling the same. The crushing plant includes a crusher and a feeding arrangement, and is driven by a diesel engine. A load value is retrieved which is related to the diesel engine e.g. by means of a J1939 interface. If the retrieved value exceeds a predetermined threshold value, the control loop of the feeding arrangement is altered. Thereby it can be avoided that the diesel engine stalls, such that continuous operation of the crushing plant may be ensured. 
     The invention is not restricted to the described embodiments and may be varied within the scope of the appended claims. 
     The disclosures in the Swedish patent application No. 0701459-0, from which this application claims priority, are incorporated herein by reference.