Abstract:
A device for detecting and adjusting the tension of a scraper chain. The device identifies broken chain as it leaves the return sprocket and enters the top race of the conveyor. When detected, the chain can be stopped automatically by the armored face conveyor control system, to avoid the potential for further damage, and warn the operators that repair of the chain is required. The device also has a conveyor with sliding frames at both ends to allow the conveyor ends to be independently adjusted to each end of the coal block, while maintaining good chain tension and control.

Description:
BACKGROUND 
     This disclosure relates to a mechanism to control the position of a scraper chain conveyor and for detection and adjustment of the tension of a scraper chain of a chain conveyor. 
     Conveyors, such as armored face conveyors, are part of an integrated longwall system that also comprises a coal-cutting machine and roof supports. As the longwall system removes mineral from the mineral block one strip (web) at a time, the load on the conveyor changes as the cutter moves along the conveyor. The conveyor progressively moves forward one web in order to reposition itself for the next cut. 
     The mineral being mined is dragged along a top race of the conveyor by a continuous chain and flight-bar assembly driven by sprockets at each end of the conveyor. More particularly, spaced apart chains, with the flight bars connecting the chains, are typical. At the delivery end, the mineral is discharged onto an adjacent conveyor while the continuous chain enters a bottom race where it proceeds to a return end, where a return end drum or sprocket reverses the direction of the chain. 
     Armored face conveyors normally operate at a fixed overall length (sprocket centers), but more usually they are fitted with an extendable return end frame. The purpose of the extendable return end frame is to take-up slack chain generated during normal operations. The variations in load and the repositioning of the many parts of the conveying system result in changes in chain tensions. To ensure slack chain is not produced, the movement of the extendable return end frame is sometimes automatically controlled to maintain a fixed chain tension. 
     This repeated action involves the repositioning of the many parts that make-up the total conveying system. Keeping the equipment inline with the coal block is difficult, as no direct steering mechanism is available with these systems. The operators have to rely on their experience by adjusting the relative position of the conveyor to the coal block to counteract a tendency of the equipment to gradually creep sideways. This inevitably results in face creep with the only corrective action available to the operators being to angle the conveyor a few degrees off square to the coal block. This is very slow and extremely difficult to gauge. 
     In certain operational situations, one of the two chains of the chain and flight bar assembly may get broken on the top race. The remaining chain can then enter the return race with the broken chain. Lower tensions in the bottom race can be contained by the single chain, which continues to the return end and then over the return end sprocket. If the broken chain is not identified on the top race, the result will be failure of the second chain, which is most likely when it approaches the discharge area. Consequence damage to related equipment can then occur. Failure is followed by prolonged down time to make a repair. Visual identification of the broken chain is possible, but is unlikely because the chain is covered with the mineral being conveyed. Additionally, on most installations, safety requirements prohibit operators from being adjacent the return end of the conveyor, which further reduces the opportunity for manual detection. 
       FIG. 1 , which is taken from Bandy U.S. Pat. No. 5,131,528, illustrates a prior art scraper chain conveyor.  FIG. 1  illustrates in simple form the various conveyor elements necessary for understanding of the conveyor equipment environment. The conveyor apparatus or assembly is shown generally by the character numeral  10  and includes a drive drum/sprocket  12  and an idler or guide drum/sprocket  14  separated by a span of a flexible conveyor  16 , illustrated partially in dashed line outline. As depicted, the conveyor  16  comprises dual conveyor chains  18  and a multiplicity of spaced flight bars  20  attached to the dual chains  18 . During operation of the conveyor assembly, the flight bars  20  push aggregate material, such as mined coal, along an underlying conveyor pan  21 . The conveyor assembly  10  is typically positioned juxtaposed to a mine wall where a seam of material is being mined for transporting the material to one end. The material is then transferred to an auxiliary conveyor for further disposition. 
     The drum/sprocket  12  is appropriately coupled to a conveyor drive motor  22 . Operation of motor  22  causes the sprocket intermeshing with the dual chains  18  to advance the conveyor  16 . A pair of sidewalls  24  forming a first portion of a “split frame” of conveyor assembly  10  serves to rotatably support the drum/sprocket  12 . The sidewalls  24  are illustrated as being telescopingly engaged with a second pair of sidewalls  26  forming a second portion of the frame and, collectively with sidewalls  24 , comprise the aforementioned split frame. The telescoping joint, indicated generally by character numeral  48 , permits the frame portions to be moved relative to one another. 
     The idler drum/sprocket  14  is appropriately mounted for rotary movement between sidewalls  26 . Relative movement at the joint  48  between the adjacent sidewalls  24  and  26  thus causes the distance span between the drum/sprockets  12  and  14  to vary accordingly. The dual conveyor chains  18  can be provided with increased or reduced tension depending upon the direction of adjusting movement of the supporting drum/sprockets with respect to each other. To provide this relative movement, assembly  10  has a tensioning means in the form of a pair of hydraulic cylinders  28  and  30 , each mounted on and secured to an adjacent sidewall  26 . In other embodiments (not shown), only a single hydraulic cylinder can be used. The cylinders have respective pistons  32  and  34 , each of which is operatively coupled to a sidewall  24  in any known and expedient manner. 
     Movement of the pistons  32  and  34  causes the first portion of the conveyor  16  represented by the side walls  24  to move longitudinally relative to the second portion and side walls  26 , thus relaxing or tensioning the chain  18 , as desired. Control of movement of pistons  32  and  34  is affected by a conventional hydraulic tensioning control circuitry, depicted generally by numeral  40  in  FIG. 1 . 
     As stated above, a certain amount of tensioning of conveyor chain  18  is essential for the proper and efficient operation of the conveyor assembly  10 . Too little tension may cause the conveyor chain to ride up the teeth of the sprockets, and even eventually, under severe conditions, become disengaged. Conversely, too much tension may cause the conveyor components to be over stressed, increasing the risk of mechanical failure in the various parts of the conveyor apparatus. 
       FIG. 2 , which is taken from Weigel et al U.S. Pat. No. 7,117,989, illustrates a prior art mechanism for controlling the tension in a scraper chain in a conveyor.  FIG. 2  shows a tensionable return station, marked as  51 , which forms the auxiliary drive of a face conveyor, and on which a spoked chain wheel  52  is located, which may be powered by drives (not shown). 
     All channel sections  70  and machine frame  51  and, where applicable, any intermediate or transitional channels located between them, have a top race  54  A and a bottom race  54  B. In top race  54  A the material to be conveyed, such as coal, is transported by means of scrapers  20  as far as the main drive, and in bottom race  54  B the scrapers run back to the auxiliary drive. The constantly changing load conditions in the top race cause the tension in the top race and bottom race sections of conveyor  16  to vary. 
     In order to detect the tension of conveyor  16 , a sensor, indicated overall by  60 , is located on the frame of return station  51 , which forms the auxiliary drive. The sensor has a sliding body or sensor body  62  with a curved sliding surface  61 , which is coupled with a shaft  63  such that it cannot be turned, said shaft reaching obliquely over the conveying trough and return trough for scraper conveyor  16  in top race  54  A of machine frame  51  of the chain conveyor. Shaft  63  is supported in bearing blocks  64 , one of which is indicated schematically at the rear side face of return station  51 . The weight of sensor body  62  causes its sliding surface  61  to be directly in contact with the upper face of a scraper  20  or with the upper face of vertical chain links  57  in the area of the measuring zone. At the same time, shaft  63 , supported in bearing blocks  64  such that it can swivel, forms a measuring shaft, and by means of shaft encoder  65  the relative position of measuring shaft  63  and thus also the relative position or swiveled position of sensor body  62  rigidly coupled with it may be detected and transmitted to the evaluation and control unit  72  via signal line  71 . Depending on the measurement signal of shaft encoder  65 , evaluation and control unit  72  then activates tensioning drive  55  of return station  51  via signal line  75 . 
     In an extensive zone within top race  54  A of return station  51 , referred to below as the measurement zone, and extending between points  67  and  68  in the drawing marked with double arrows, scraper conveyor  16  has vertical play. In other words, between point  67  and point  68  along the track in top race  54  A, conveyor  16  can essentially move freely in a vertical direction, i.e. perpendicularly to the bottom of top race  73 ,  74 . 
     In the embodiment shown, the scraper chain is running with optimum tension, i.e. some chain links in the measuring zone are slightly lifted away from the bottom of top race  74 . When the chain is dangling, on the other hand, chain links  57 ,  58  and scrapers  59  within the area of the measuring zone and in the area of the machine frame are in contact at every point with the bottom of top race  73  or  74  of return station  51 , and sensor body  62  is at its largest downwards deflection. This state is detected by evaluation and control device  72  and tensioning drive  55  is extended. If the tension of scraper conveyor  16  increases, vertical and horizontal chain links  57 ,  58  together with scrapers  59  of scraper conveyor  16  may move even higher in the measuring zone, due to the absence of restrictive guidance and the existing vertical play ( 67  or  68 ), which causes sensor body  62  to be swiveled clockwise and this deflection to be detected by shaft encoder  65  and transmitted to evaluation and control device  72  as a measurement signal. If the chain reaches a preset tension corresponding to that of a tight chain, this is detected directly by shaft encoder  65  as a result of the greater deflection of sensor body  62 , and evaluation and control device  72  then activates tensioning drive  55 , in some cases via a closed-loop control algorithm, through signal line  75  such that tensioning cylinder  56  is retracted in order to reduce the tension in scraper conveyor  16 . 
     Other mechanisms for monitoring chain tension include U.S. Pat. No. 5,505,293, and U.S. Pat. No. 4,657,131. 
     SUMMARY 
     This disclosure takes as its starting point the typical longwall conveyor described above where the delivery end is fixed and the return end has a telescopic sliding frame. The principal object of this disclosure is to provide a device for detecting and adjusting the tension of the scraper chain, which determines the tension reliably and simply. Another object of this disclosure is to provide such a device that reliably senses chain tension while at the same time not adversely affecting the chain path. 
     This disclosure also provides a means of identifying broken chain as it leaves the return sprocket and enters the top race of the conveyor. When detected, the chain can be stopped automatically by the armored face conveyor control system, to avoid the potential for further damage, and warn the operators that repair of the chain is required. 
     Another principal object of this disclosure is to provide sliding frames at both ends of the conveyor to allow the conveyor ends to be independently adjusted to each end of the coal block, whilst maintaining good chain tension and control. 
     Providing the delivery and return end frames with a telescopic section addresses the problem of face creep by allowing the operator to quickly adjust the position of both ends of the conveyor, thus offsetting the effects of face creep. This is particularly critical on conventional end discharge conveyor systems, where the correct relationship between the longwall discharge conveyor and an auxiliary cross conveyor (beam stage loader) must be maintained. This problem becomes even more critical where there are two longwall conveyors operating side by side, which is often the case with sub-level caving or longwall to coal caving. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a plan view of a prior art delivery discharge end scraper chain conveyor arrangement. 
         FIG. 2  is a schematic view of a prior art tension sensor for detecting and tensioning a scraper chain. 
         FIG. 3  is a plan view of an improved tension sensor. 
         FIG. 4  is a perspective view of an alternate embodiment of the tension sensor shown in  FIG. 3 . 
         FIG. 5  is a perspective view of the tension sensor shown in  FIG. 4 , as mounted at the return end of a conveyor. 
         FIG. 6  is a perspective view of a load cell used in the tension sensor of  FIGS. 4 and 5 . 
         FIG. 7  is a schematic top view of the chain, two tension sensors and a tension control. 
         FIG. 8  is a top view of a conveyor and a secondary or auxiliary conveyor. 
         FIG. 9  is a side view of the conveyor and auxiliary conveyor shown in  FIG. 8 . 
         FIG. 10  is a top view of a double conveyor system. 
     
    
    
     Before one embodiment of the disclosure is explained in detail, it is to be understood that the disclosure is not limited in its application to the details of the construction and the arrangements of components set forth in the following description or illustrated in the drawings. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Use of “including” and “comprising” and variations thereof as used herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Use of “consisting of” and variations thereof as used herein is meant to encompass only the items listed thereafter and equivalents thereof. Further, it is to be understood that such terms as “forward”, “rearward”, “left”, “right”, “upward” and “downward”, etc., are words of convenience and are not to be construed as limiting terms. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 3  illustrates an improved version of the tension sensing means  60  shown in  FIG. 2 . Conventionally, to allow for optimum use of the length of the tailgate or return end or station  51 , a wear strip  101  is installed to guide the conveyor  16  down to the track or race  54  A level. The tensioning means, or tension sensor  104 , of  FIG. 3 , comprises a wear strip  101  including a wear plate  108  that contacts the top surface of the conveyor  16 . 
     The wear plate  108  is supported by a wear strip support  112 , and the wear plate  108  is connected to the wear strip support  112  by a pin  116  at one end and a load-sensing pin  120  at the other end. The wear plate  108  engages the top surface of the conveyor  16 , and changes the path or trajectory of the movement of the conveyor  16 . This contact and change in direction of the conveyor  16  causes a force to be applied on the wear plate  108 . The load-sensing pin  120  that connects the wear plate  108  to the wear strip support  112  senses this force. The output from the load-sensing pin  120  is then be used to determine the tension of the conveyor  16 , and to adjust the tension, as needed, using any conventional chain tensioning system, such as the joint  48  and pistons  32  and  34  and circuitry of  FIG. 1 . 
     An alternate and preferred embodiment  124  of the tension sensor is illustrated in  FIG. 4 . In  FIG. 4 , a load cell  128  is located between a wear plate  132  and a wear strip support  136 . The load cell  128 , which is illustrated in  FIG. 6 , is a cylinder including a plurality of spaced apart passageways  130  through the cylinder. Within the passageways are load sensors (not shown), which measure the compression force on the load cell  128 . By placing the load cell  128  between the wear plate  132  and the wear strip support  136 , the load cell  128  responds to the force applied to the wear plate  132  by the conveyor  16 . In order to provide redundancy, as shown in the preferred embodiment illustrated in  FIG. 4 , two spaced apart load cells  128  are placed between the wear plate  132  and the wear strip support  136 . More particularly, the wear strip support  136  includes a cavity  138  that receives the load cells  128 , and the wear plate  132  is connected to the wear strip support  136  by means of a screw  140 . 
       FIG. 5  illustrates a perspective view of the load sensor  124  mounted on the conveyor apparatus  10  at the return end  51 . As shown, the cavity  138  receiving the load cells  128  can be formed by a plate  142  secured to the wear strip support  36 . This provides ready access to the load cells  128  from adjacent the conveyor apparatus  10 , without the need for significant disassembly of conveyor parts. This thus permits ready access and repair of the tension sensor  124 , when the need arises. 
     The disclosure also illustrates, in  FIG. 7 , the providing of two such tension sensors on such a conveyor apparatus  10 . More particularly, in this embodiment, the conveyor  16  includes the two spaced apart chains  18 , and the plurality of flights or flight bars  20  that are connected and spaced apart but between the two chains  18 . Each conveyor flight  20  has a first end and a second end. Each flight bar end is spaced apart from its respective adjacent chain. A tension sensor, such as the tension sensor illustrated in  FIGS. 2 ,  3  and  4  above, is provided in a respective wear strip for each one of the two conveyor chains  18 . Each tension sensor  124  is electrically connected via a line  154  to a comparator  158 . 
     In the preferred embodiment, as illustrated in  FIG. 7 , the part of the conveyor that contacts the tension sensor  124  is the end or tip of the flight bar  20 . In other embodiments, not shown, a tension sensor  124  can be placed above each of the chains, instead of the flight tips. The tip of the flight bar  20  will only contact the wear strip intermittently. As a result, the tension sensor  124  will only produce intermittent signals. 
     To eliminate transient load spikes and to allow for the odd missing flight bar  20 , the tension sensor  124  collects a rolling average reading over 20 or so flight bars. As each flight bar tip passes along the load sensor, even at a constant chain tension, the signal varies due to the changing geometry of the system. The tension sensor  124  records the peak signal value as each flight bar  20  passes over the wear plate  132 . If the rolling average peak reading is too low, then the tension means moves the joint  48  to stretch the chain, or vice versa. The tension means is initialized by establishing a required peak signal value by stopping the conveyor with a flight bar under the sensor, fitting a temporary load transducer to the chain itself, and then moving the joint  48  to tension the static chain. When the chain is at the required tension, the tension sensor  124  stores the signal, and it is this signal value that the tension sensor  124  maintains while the conveyor is running. 
     The above overview is a simplified version of the sensor signal management system, and applies to steady chain load increase or decrease during the coal cutting cycle. The tension sensor  124  must also deal with special events such as starting a full conveyor or the rapid unloading of a conveyor, like when the shearer stops cutting. Collecting a rolling average signal cannot respond quickly enough to deal with these events, so advance action must be taken. For example, the sprocket is extended to significantly stretch the chain before loaded conveyor startup to prevent generation of slack chain. 
     In the event of a chain break, the tension in the two chains  18  will be different. The outputs of the tension sensors  124  are compared by a comparing means, comparator  158 , and in the event of a significant difference, the operation of the conveying apparatus  10  can be stopped so the broken chain can be repaired. In the preferred embodiment, the tension sensors  124  are provided adjacent the top race of the return end of the conveyor apparatus. If additional sensors or sensing of the tension at other locations in the conveying apparatus is desired, other tension sensors  124 , in other locations, can be used. The use of the two tension sensors  124  is also beneficial, for the output from the tension sensors  124  can be averaged to produce a more accurate indication of overall conveyor tension. The comparator  158  forms a part of the chain tensioning system such as the joint  48  and pistons  32  and  34  and circuitry of  FIG. 1 . 
     As illustrated in  FIG. 8 , an auxiliary or secondary conveyor  200  is located at one end of a conveyor apparatus  210 . The material on the conveyor  16  leaves the conveyor and is dumped onto the auxiliary conveyor  200 . During operation of the conveyor apparatus  210 , the location of the conveyor apparatus  210  may move relative to the location of the auxiliary conveyor  200 . Currently, operators need to make various adjustments in order to try to accommodate such movement. This can result in difficulty maintaining conveyor operation. 
     The improvement in this disclosure is, in order to accommodate some movement of the conveyor apparatus  210  relative to the auxiliary conveyor  200 , the conveyor apparatus frame accommodates sliding movement at both ends. At one end, the sliding movement adjusts the tension of the conveyor  16 , and sliding movement at the other end accommodates movement of the conveyor apparatus  210  relative to the auxiliary conveyor  200 . If the conveyor apparatus  210  moves relative to the auxiliary conveyor  200 , an operator can move the sliding end of the conveyor  210  adjacent the auxiliary conveyor  200 . Movement of the sliding end of the conveyor  210  can also be occasioned by the use of tensioning means, as described hereinafter, as used on the tensioning end  51  of the conveyor  16 . Only in this instance, the movement is not intended to effect the tension of the conveyor  16 , but the location of the end of the conveyor apparatus  210  relative to the auxiliary conveyor  200 . When movement at this end of the conveyor occurs, the chain tension does change, so the other end of the conveyor apparatus  210  is adjusted by the automatic tensioning means to return the conveyor  16  back to the appropriate tension. Movement of the sliding end of the conveyor  210  adjacent the auxiliary conveyor  200  much overcome the maximum working chain tensions (which are at there highest as these top chains reach this frame; plus significant sliding friction due to the typical large size and weight of the Main gate equipment. 
     More particularly, a driven drum/sprocket  312  is appropriately coupled to a conveyor drive motor  322 . Operation of motor  322  causes the sprocket intermeshing with the dual chains  18  to advance the conveyor  16 . More particularly, as illustrated in  FIGS. 8 and 11 , in addition to the hydraulic pistons  32  and  34  spanning the joint  48  at the return end  51 , a pair of sidewalls  324  forming a first portion of a “split frame” of the main gate end of the conveyor apparatus serves to rotatably support the drum/sprocket  312 . The sidewalls  324  are illustrated as being telescopingly engaged with a second pair of sidewalls  326  forming a second portion of the frame and, which collectively with sidewalls  324 , comprise the aforementioned split frame. The telescoping joint, indicated generally by character numeral  348 , permits the frame portions to be moved relative to one another. 
     Relative movement at the joint  348  between the adjacent sidewalls  324  and  326  thus causes the distance span between the drum/sprockets  312  and  14  to vary accordingly. The conveyor  16  can be provided with increased or reduced tension depending upon the direction of adjusting movement of the supporting drum/sprockets with respect to each other. To provide this relative movement, the conveyor assembly  310  has a pair of hydraulic cylinders  328  and  330 , each mounted on and secured to an adjacent sidewall  326 . The cylinders have respective pistons  332  and  334 , each of which is operatively coupled to a sidewall  324  in any known and expedient manner. 
     The location of the conveyor apparatus relative to the auxiliary conveyor is further illustrated in  FIG. 9 . If desired, in lieu of operator correction of the location of the conveyor apparatus, the conveyor apparatus can be physically connected by a bar  352  to the auxiliary conveyor. In this instance, tension is maintained at this end of the conveyor by some tensioning means, such as the tensioning means previously described. But in order to accommodate some movement in the event the auxiliary conveyor and main conveyor change location, either a hydraulic accumulator (now shown), or some relief valve (now shown) must be provided in the hydraulic tensioning means in order to allow for the movement of this sliding end of the conveyor apparatus  210 . When this end of the conveyor apparatus  210  adjusts by movement of the auxiliary conveyor  200 , then tension is corrected, as described before, by the return end  51 . 
     The problem of conveyor apparatus movement relative to the auxiliary conveyor is especially relevant where a pair of conveyor apparatus is used. As illustrated in  FIGS. 10  A and  10  B, it is known to use one conveyor adjacent a coal face, and a second conveyor apparatus behind the roof supports to collect coal that falls from the longwall roof as the longwall advances. In this instance, the double sliding frame ends would be used with both conveyor apparatus. 
     Additionally the frame-sliding  48  and  348  can be adjusted to correctly align the conveyor end with both edges of the coal block, moving both the return end frame and delivery end frame at the same time to maintain correct chain tension during this adjustment. This would not be a normal requirement or mode of operation as the position of the Return End Frame to coal block is less critical in most cases. 
     This aspect of the disclosure thus has the following benefits. Manual or automatic control of the delivery end frame sliding module makes fine adjustments for optimum discharge of material from the extendable longwall armored face conveyor to the cross beam stage loader conveyor. 
     Since the changes in the overall length of the conveyor, as a result of adjusting the delivery end sliding frame module will change the chain tension, adjustments must be in small increments and effected slowly to give the automatic chain tensioning system time to react. At all times it is the automatic chain tensioning system that controls and maintains correct chain tension, not the adjustment of the delivery end frame module. 
     Various other features and advantages of the disclosure will be apparent from the following claims.