US3378303A

US3378303A - Method and apparatus for controlling loading machines in underground mining

Info

Publication number: US3378303A
Application number: US563470A
Authority: US
Inventors: Weber Karl-Heinz
Original assignee: Gebr Eickhoff Maschinenfabrik u Eisengiesserei GmbH
Current assignee: Gebr Eickhoff Maschinenfabrik u Eisengiesserei GmbH
Priority date: 1965-07-07
Filing date: 1966-07-07
Publication date: 1968-04-16
Anticipated expiration: 1985-04-16
Also published as: DE1231646B; GB1106410A

Description

April 16, 1968 KARLHEINZ WEBER METHOD AND APPARATUS FOR CONTROLLING LOADING MACHINES IN UNDERGROUND MINING 3 Sheets-Sheet 1 Filed July 7. 1966 mmdim mmJDa mmPzDOO METHOD AND APPARATUS FOR CONTROLLING LOADING MACHINES 1N UNDERGROUND MINING 5 Sheets-Sheet 2 Filed July 7, 1966 EN EN @IN mozmmw N 5.5300 @mm mozmmmh mm mi mmh/500 P Umm ESSO@ .su o :i N m mmm NNM/ 5m Nm s2 E@ mK otm otmS J i522 .522 x mm z mmE/z f k f vm mmnxw mIw m23@ m23@ f om mv C m oN L Nm APU] 16, 1968 KARL-HEINZ WEBER 3,378,303

METHOD AND APPARATUS FOR CONTROLLING LOADING MACHINES IN UNDERGROUND MINING Filed July 7, 1966 3 Sheets-Sheet INVENTOR Karl-Heinz Weber United States Patent O 3,378,303 METHOD AND APPARATUS FOR CONTROL- LING LGADING MACHINES IN UNDER- GROUND MINING Karl-Heinz Weber, Witten-Eleven, Germany, assignor to Gebr. Eickhoi Maschinenfabrik und Eisengiesserei m.b.H., Bochum, Germany, a corporation of Germany Filed July 7, 1966, Ser. No. 563,470 Claims priority, application Germany, July 7, 1965, E 29.663 7 Claims. (Cl. 299-1) This invention relates to mining, notably coal mining, and, more particularly, to controlling loading machines that are disposed along a movable conveyoi and hauled therealong by, for example, means of a winch, or a mining machine that advances in front of the conveyor along a face of a mineral seam to be mined.

Loading machines of the conventional type comprise a plurality of serially-linked members, each comprising at least one scraping shoe or scoop projecting towards the face of the mineral vein or seam to be mined and having inclined surfaces that rise from the seam floor to the upper edge of the conveyor for receiving the broken mineral, such as coal, lbetween the seam face and the conveyor and delivering it to the conveyor. During the loading phase, the loading machine extends along that section of the conveyor which is being pushed gradually toward the most recently exposed coal face by means of thrust means, for example a plurality of thrust cylinders and associated pistons and piston rods. Within this section, the loading machine is in a constant to and fro motion, the motion being limited on the one hand -by the preceding mining machine, and on the other by the coal face and the conveyor that follows the mining machine and is pushed continuously toward the coal face such that it gradually approaches the coal face as the distance therealong from the mining machine increases. The area defined between the coal face and the conveyor section that gradually approaches the coal face as the distance from the mining machine increases, is also referred to as the recovery area. In prior art mining operations, the to and ro motion of the loading machine is supervised and controlled by an attendant; i.e., he should reverse the direction of the movement of the loading machine whenever the loading machine approaches that portion of the recovery area that is narrower than the width of the loading machine and whenever the loading machine approaches the mining machine in order to avoid engagement between the loading machine and the mining machine and to prevent jamming of the loading machine between the conveyor and the coal face. The manual control of the loading machine requires great skill and does not always assure trouble-free operation, the ditliculties stemming primarily from the fact that the attendant is unable to determine the precise location of the loading machine which is buried under the pile of broken coal while in motion. Indeed, the attendant can only roughly estimate the location of the loading machine from the manner in which the .pile of `broken coal moves under the influnce of the moving loading machine buried therein.

It is an object of the present invention to provide automatic control of the loading machine whereby during operation a collision between the loading machine and the mining machine and locking or jamming of the loading machine between the face of the mined seam and the conveyor are effectively prevented.

The invention, brietiy, accomplishes this object by producing first and second quantities by means of first and second position indicating means responsive to the motion of the loading machine along the conveyor and the motion of the mining machine along the mineral seam respec- 3,378,303 Patented Apr. 16, 1968 ICC tively, producing a first control signal when the difference between said first and second quantities coincides with a rst reference quantity that corresponds to a predetermined maximum distance between said mining and loading machines, producing a second control signal when the diierence between said irst and second quantities coincides with a second reference quantity that corresponde to a predetermined minimum distance between said mining and loading machines, and changing the operating conditions ofthe drive means for the loading machine in response to said lirst and second control signals respectively for limiting the motion of said loading machine between said predetermined maximum and minimum distances. The drive means may either be shut down whenever any one of the first and second control signals occurs, or it may be transferred from its one operating direction to its opposite operating direction in response to said lirst control signal and from its opposite operating direction to its one operating direction in response to said second control signal, Since shut down or reversal of the drive means at the proper instants is accomplished automatically, no attendant is required for controlling the to and fro motion of the loading means, and collision between the mining machine and the loading machine and jamming of the latter are effectively prevented.

In accordance with the modification of this invention the operation of the loading machine, as it moves away from the mining machine, may be controlled such that the greatest distance between the mining machine and the loading machine is rendered dependent upon either that section of the conveyor or that section of the mine roof support structure which has been pushed into the most forward position closely adjacent the most recently exposed seam tace, thereby insuring the moving loading machine covers just that portion of the recovery area where the vconveyor has not yet reached its most forward position. The roof support structure, following the mining machine, is pushed continuously toward the seam face, the movement of the roof support structure being coordinated with that of the conveyor toward the seam face, or the support structure and conveyor being pushed simultaneously toward the seam face, and this motion toward the seam face being either controlled from or indicated at the roadway. In practicing this modication, the drive means for the loading machine may be reversed or shut down` in response to that support structure section or conveyor section which has completed its advance toward the most recently exposed seam face and is closest to the mining machine, i.e., that section which at any time during operation defines the trailing end of the recovery area, said section hereinafter referred to as the terminal section. As the mining machine advances` along a previously exposed seam face and the various sections of the sup- -port structure and conveyor are pushed sequentially toward the newly exposed seam tace such that the recovery area in effect advances along with the mining machine, the terminal section may, in effect, also be considered as foilowing the advancing mining machine. In this manner, the travel path of the loading machine is determined at any time by the effective length of the recovery area, and the loading machine performs the to and fro motion at all times along those sections of the conveyor which are in the process of being pushed toward the seam face whereby the pile of broken minerals in front of those conveyor sections is loosened up further and supplied to the upper edge of the conveyor.

In order to render the travel path oi the loading machine responsive to the eiective length of the recovery area at any time, an indicating means may be provided for indicating continuously the distance between the roadway and the section of the roof support structure or conveyor pushed last, i.e., the above-referred to terminal section, said indicating means producing a quantity corresponding to said distance. By means of a difference counter responsive to the last-named quantity and the quantity produced by the aforesaid first position indicating means, a control signal is produced when the computed difference between the two quantities coincides with a reference quantity that corresponds to the minimum distance that must be present between the seam face and the conveyor in order to enable the loading machine to carry out its to and fro motion. The lastnamed reference quantity is, of course, determined primarily by the width of the loading machine and also by the curvature the conveyor sections may assume when being pushed toward the seam face. Whenever the control signal occurs, the drive means is either shut down or reversed.

Further advantages and objects of the Ipresent invention Will become more readily apparent from the following description and the accompanying drawings, in which:

FIGURE l shows schematically a mining machine together with the associated conveyor and loading machine and the control system for automatically controlling the loading machine in accordance with this invention;

FIG. 2 shows schematically a mining machine together with the associated conveyor and loading machine and a modification of the control system for automatically controlling the loading machine in accordance with this invention; and

FIG. 3 Shows in greater details a portion of FIG. 2.

Referring to FlG. l, the arrow 1t) denotes the direction in which a mining machine 11 that may be movable on a track or guideway 11a, advances along a face 12 of a mineral vein 13, which is the shown embodiment is a coal, vein, that extends from a roadway 14 to another roadway (not shown) spaced from the roadway 14. The mining machine 11 which per se forms no part of the present invention, is equipped with a cutting roller 15 that exposes a new coal face 16 as the mining machine 11 advinces along the coal face 12 which has been exposed by a preceding cut, the new coal face 16 beginning at the roadway 14 and the previously exposed or old coal face 12 terminating at the other roadway (not shown), Advancement of the mining machine 11 along the old coal face 12 may be effected by a so-called winch motor (not shown) disposed on the mining machine, said winch motor driving a chain wheel 17 which is in engagement with a chain 18 that is anchored with one end thereof in the roadway 14. The chain 18 is looped about a guide chain wheel 19 and anchored with its other end in the other t roadway (not shown). In order to transport the mined coal away from the mining station, a conveyor 20 is installed, the conveyor extending essentially along the coal face 16, the conveyor per se forming no part of the present invention. A suitable conveyor is the so-called dualchain scraper flight conveyor that includes a plurality of serially-arranged conveyor or scraper elements 21 and a pair of continuous chains 22 carrying the scraper elements 21 and being driven by a pair of chain wheels 23 which, in turn, are driven by a motor 24 such that the upper strands of the chains 22 move in the direction of the arrow 25 and the lower strands move in the opposite direction.

In order to deliver the broken coal cut by the cutting roller 15 to the conveyor elements 21, a loading machine 26 is provided that comprises a plurality of seriallyarranged scoops 27 carried by a continuous hauling means 28, for example, a chain or rope, that may be looped about both a drive pulley or drum 29 installed in the roadway 14 and a return pulley or drum (not shown) located in the other roadway, the loading machine 26 being driven by a motor 30 installed in the roadway 14. In operation, the motor 30 is controlled such that the loading machine 26 carries out n to and iro motion over a predetermined distance, for example, l0 to l5 meters.

n, P ad Each scoop is provided with a sloping surface 27a declining toward the coal face 16 and a pair of laterally declining slopes 27b ln operation, the conveyor 20 and the loading machine 26 are pushed gradually against the newly exposed coal face 16 by means of thrust means, for example, a plurality of thrust cylinders 31 and associated pistons (not shown) and piston rods 32, only two of which are illustrated schematically in FIG. l.

According to the present invention, the to and fro motion of the loading machine 26 is confined to that section of the recovery area between the conveyor and the new coal tace where the conveyor is still spaced a certain distance from the coal face, thereby preventing locking of the loading machine between the coal face and the conveyor. This is accomplished by reversing continually the drive motor 36 for the drive pulley 29 from time-to-tirne such that the loading machine 26 advances for a period of time in the direction of the arrow 10 and thereafter for a period of time in the direction of the arrow 25, the motion in the direction of the arrow 1t) being limited by the position ot the cutting roller 15, and the motion in the opposite direction being limited by the conveyor section advanced to a position -closely spaced from the coal face.

In accordance with the teachings of the present invention, the to and fro motion is controlled automatically; i.e., the motion of the loading machine 26 in the direction of the arrow 10 is to be reversed as soon as the front scoop thereof approaches the cutting roller 15, and the motion in the opposite direction as indicated by Athe arrow 25 is again to be reversed after traveling a predetermined distance, for example, l0 to l2 meters, in said opposite direction.

An exemplary apparatus for automatically controlling the to and fro motion of the loading machine includes a difference counter 33, two

counters

34 and 35 having their ou-tputs electrically connected to the inputs of the difference counter 33, and a pair of switching relays 36 electrically connected to the difference counter 33 to be responsive to the outputs thereof, the switching relays 36 being operatively connected to the mctor 3() for reversing the operation of the latter from the one direction to the other and vice versa, respectively. The difference counter 33 and the

counters

34 and 35 are installed preferably in the roadway 14. The apparatus includes also pulse generating means 37 and 38 for producing voltage pulses in response to rotary motion of the chain wheel 17. In a specific embodiment of the invention, each pulse generating means may comprise an alternating current energized coil positioned adjacent the chain wheel 17, the latter being provided with a plurality of damping means (not shown) for varying the characteristic of each coil 'as the damping means approach and move away from the coils while rotary motion of the chain wheel 17 is in progress. The relative position of the coils and the chain wheel 17 is such that the damping means, upon passing the coils, generate in each coil a train of voltage pulses, with the pulses in one of the coils lagging in time with respect to but overlapping the pulses in the other coil. The outputs of the pulse generating means 37 and 3S are connected respectively to pulse Shapers 39 and 4tfor connecting the voltage pulses into substantially rectangular pulses. The output of the pulse shaper 39 is connected to both a first input of a two-input AND gate 41 and a first input of another two-input AND gate 42. The output of the pulse Shaper 4t? is connected directly to the input of a first multivibrator 43 and, through an inverter stage 44, to the input of a second multivibrator 45, the output of the multivibrator 43 being connected to the second input of the AND gate 42, and the output of the multivibrator 45 being connected to the second input of the AND gate 41. Because of the presence of the inverter stage 44, the

multivibrators

43 and 45 will be responsive 'to the rising and declining lanks respectively of the pulses 4derived from the pulse 5 Shaper 49 and produce attheir output pulses, with the output pulses of the multivibrator 45 `being displaced in time with respect to the output pulses ot the multivibrator 43, the displacement being determined by the pulse duration of the pulses at the output of the pulse shaper 40. As stated before, the voltage pulses produced in the

pulse generating lmeans

37 and 38 are overlapping. Hence, depending upon the direction of rotation of the chain wheel 17, two pulses appear simultaneously at 'both inputs of one of the AND gates whereas, at the same time, the other one of the AND gates has applied a pulse to only one of its two inputs. Upon rotation of the chain wheel 17 in the direction 17a, the pulses generated in lthe pulse generating means 38 precede the pulses generated in the pulse generating means 37 while, upon rotation in the reverse direction, the pulses of the pulse generating means 38 are lagging with respect to those of the means 37. Specifically, with the chain wheel 17 rotating in the direction of the arrow 17a, the declining ilank of the preceding pulse derived from the pulse generating means 38 falls within the time interval during which a lagging pulse derived from the pulse generating means 37 is present whereas, upon rotation of the chain wheel 17 in the reverse direction, the rising flank of the now lagging pulse derived from the means 38 falls within the time interval during which a now leading pulse derived from the means 37 is present. The elements 33 through 45 per se are known in the art and, hence, will not be described herein in greater detail. In the illustrated embodiment, with the chain wheel 17 rotating in the direction of the arrow 17a, the AND gate 41 has applied pulse signals to both inputs, the AND gate 41 thus producing an output pulse signal that is applied to the `counter 34, for example, through one of the conductors 46. Upon rotation ofthe chain wheel 17 in the reverse direction, the AND gate 41 is blocked, and the AND gate 42 produces an output pulse signal which is applied to the counter 34, for example, through the other one of the conductors 46. Thus, the counter 34 is responsive to the motion of the mining machine l1 along the coal face and registers or indicates continuously the location of the mining machine, i.e., the distance thereof from the roadway 14. The conductors 46 are preferably included in the utility cable that may also contain the power supply and other control conductors `for the rnotors of the mining machine.

According to the invention a corresponding circuit arrangement is also provided for determining the revolutions and direction of rotation :of the drive pulley 29 that is driven by the motor 3i?, said pulley having distributed at its periphery damping means (not shown) for affecting the characteristics of a pair of adjacently-disposed pulse generating means 47 and 4S in the manner set forth above in connection with the pulse generating means 37 and 38. The outputs of the pulse generating means 47 and 48 are connected respectively to pulse

shapers

49 and 50, the output of the pulse shaper 49 being connected directly to both a first input of a two-input AND gate 51 and a first input of another two-input AND gate 52. The output ot the pulse Shaper Sil is connected directly to the input of a multivibrator 513 and, through an inverter stage 54,

to the input of a multivibrator 55, the output of the multi-- vibrator 53 being connected to the second input of the AND gate 52, and the output of the multivibrator 55 being connected to the second input of the AND gate 51. The outputs of the AND gates 51 and 5-2 `are connected to the counter 35. The operation of the elements 47 through `5S and 35 in response to the rotary motion of the drive pulley 29 is similar to that of the elements 37 through 45 and 34 and, hence, will not be described herein aga-in. It is believed readily apparent that the counter 35 is responsive -to the motion of the loading machine 25 and registers or indicates continuously the location thereof7 i.e., the distance between the roadway 14 and the loading machine 26. Both counters 34 and 35 are operatively connected to the difference counter 33 in which the difference between the two output magnitudes from the

counters

34 and 35 is computed and registered continuously. The difference coun-ter 33 is designed or preset for producing a first output signal when the computed difference coincides with a first refe-rence value and a second output signal when the computed difference coincides with a second reference Value, the iirst and second reference values corresponding respectively -to the predetermined permissible maximum and minimum distances between the mining and loading machines. The difference values computed continuously by the difference counter 33 correspond, of course, at .any instant -to the distance between the loading machine and the mining machine. Accordingly, when in operation the loading machine 26 has traveled a predetermined distance in the direction of the arrow 25, the difference counter 33 produces a first output signal which, in the shown embodiment, is applied to the left-hand switching relay 36 for reversing the motor 3i! from the one operating direction to the other, thereby reversing the direction of motion of the loading machine 26, or for shutting down said motor 3i), if desired. As soon as the loading machine 26, now traveling in the direction of the -arrow 10, approaches a predetermined minimum distance from the mining machine, the difference counter 33 produces a second output signal that is applied to the right-hand switching relay 36 for reversing the motor 30 from said other tto said one operating direction, or for again shutting down said motor 30, if desired.

In the embodiment illustrated in FIG. 2, the effective operating range of the loading machine 26 is controlled also in response to the operation of the thrust cylinders 31 (only some of which are shown) that are eifective t0 push the mining equipment including the conveyor 2t) and the mine roof support structure having support beams 7i?, some of which are shown, toward the new coal face 16, thereby limiting the effective operating range of the loading machine essentially to that section of the recovery area where broken coal is still present. This may be accomplished by reversing the motor 3? in response to the thrust motion of the thrust cylinder piston rods 32 that push the roof support structure against the new coal `face 15, after the loading machine 26 has traveled a certain distance in the direction of the arrow 25. Thus, the traveling path of the loading machine 26 may be restricted at all times by one of the cylinders, the piston rod 32 of which has reached its fully extended position last. For this purpose, the piston rods 32 are provided with ledges 7i, shown in FIG. 3, for operating switches 72 (only two of which are shown in FIG. 2) in a control circuit 73 that is operatively connected to a counter 74, the apparatus, for example, being so designed that the counter 74 is activated whenever a piston rod reaches its fully extended position and engages its associated switch 72. Thus, the counter 74 effectively indicates continually the dist-ance between the roadway 14 and that thrust cylinder the piston rod of which has reached its fully extended position last and, hence, the dis-tance between the roadway .and the afore-dened terminal section. The output of the counter 74 is connected to one input of a difference counter 33a. The counter 35' is responsive to the rotary motion of the drive pulley 29, as described more fully in connection with FIG. l, and operative to indicate continuously the actual position of the loading machine 25, the output of said counter 35 being connected to another input of the difference counter 33a and also to an input of a -dilerence counter 33h. The outputs of the difference counters 33a and 33h are connected respectively through the switching relays 36a and 36]; to the motor 30 for reversing the operation of the latter. Otherwise, FIG. 2 is similar' to FIG. l, like reference numerals being employed in both figures -to denote the same elements. The difference counter 33a computes and registers the difference between the outputs from the counters 74 and 3S and is designed for producing an output signal whenever the difference coincides with a reference quantity corresponding to the permissible minimum distance between the conveyor and the coal face to permit to and fro motion ofthe loading machine. Whenever this output signal occurs, the switching relay 36a responsive thereto becomes effective to reverse the operation of the motor 30 or, if desired, to shut it down, thereby effectively llimiting the greatest distance of the loading machine 26 from the mining machine 1l, such reversal or shut down being effected before any locking or jamming of the loading machine 26 between the conveyor Ztl and the coal face 16 can occur. The difference counter 33b is designed for producing an output signal whenever the difference between the outputs `from the

counters

34 and 35 coincides with the aforedescribed second reference value. Whenever the last-named output signal occurs, the switching relay 36h in response thereto effects reversal or shut down of the motor .30 when the loading machine has reached its shortest predetermined distance from the mining niachine 11, thereby effectively preventing any collision between tlie loading and mining machines.

According to another modification of this invention, the greatest permissible distance between the mining and loading machines may also be limited in response to the control system for controlling, from the roadway, the operation of the thrust cylinders and pistons that push the seam roof support structure and the conveyor toward the seam face. This may be accomplished by applying to a dif ference counter, preferably on termination of the thrust operation, whenever the rod support structure section or conveyor section pushed last has reached its closest position relative to the seam face, a quantity that corresponds to the distance between the roadway and said section pushed last, the difference counter being also rendered responsive to the quantity from the position indicating means associated with the mining machine, and being effective to produce an output signal for either reversing the drive means of the loading machine or shutting it down Whenever the latter has reached the greatest permissible distance from the mining machine. Reversal or shut down of the drive means whenever the loading machine has reached the smallest permissible distance from the mining machine, may be effected as described before. This Inode of controlling the operation of the loading machine is particularly suitable in connection with mechanized mining Where no attendant is present at the mining station, the operation of the thrust means for advancing the seam roof support structure and the conveyor being controlled from the roadway. One advantage of this modification resides in the fact that the control system 4for controlling the operation of the thrust means is used to perform a position indicating function which in the embodiments described above has been performed by a separate indicating system.

While the invention has been described in connection with specific embodiments, it will be apparent to those skilled in the art that various modifications may be made without departing from the spirit and scope thereof, and while the invention has been described to some extent specifically with respect to coal mining, it should be understood that it is applicable also to mining other minerals.

l claim as my invention:

1. Method for controlling the operation of a loading machine for receiving mineral mined by a mining machine that advances in front of the loading machine along a mineral seam and delivering the mined mineral to a conveyor the sections of which following the advancing mining machine are pushed gradually and sequentially toward a seam face exposed by the mining machine, the loading machine being disposed between the exposed seam face and the conveyor and being driven by drive means to carry out a to and fro motion along said conveyor, said method comprising the steps of producing a first quantity by means of a first position indicating means responsive to the motion of the loading machine along the conveyor, producing a second quantity by means of a second position indicating means responsive to the motion of the mining machine along the mineral seam, producing a first control signal when the difference between said first and second quantities coincides with a first reference quantity that corresponds to a predetermined maximum distance between said mining and loading machines, producing a second control signal when the difference between said first and second quantities coincides with a second reference quantity that corresponds to a predetermined minimum distance between said mining and loading machines, and changing the operating conditions of said drive means in response to said first and second control signals respectively for limiting the motion of said loading machine between said predetermined maximum and minimum distances.

2. The method of claim l, wherein, in response to said first control signal, said drive means is controlled to transfer from a motion in one direction to a motion in the opposite direction, and wherein, in response to said second control signal, said drive means is controlled to transfer from the motion in said opposite direction to the motion in said one direction.

3. The method of claim l, wherein said drive means is shut down in response to at least one of said first and second control signals.

4. The method of claim 1 wherein the conveyor sections are pushed toward a seam face by thrust means and the roof of the seam over the mined area is supported by a roof support structure that is advanced section by section sequentially by said thrust means toward the seam face as the conveyor is being pushed toward the seam face, the method including the step of producing a third quantity response to the location of the hereinbefore terminal section of said conveyor and roof support structure at any time during operation, the first control signal being produced in response to said first and third quantities when the loading machine approaches said terminal section.

5. Apparatus for controlling the operation of a loading machine that receives minerals mined by a mining machine advancing in front of the loading machine along a mineral seam and delivers the mined minerals to a conveyor the sections of which, following the mining machine, are pushed gradually and sequentially toward a seam face exposed by the mining machine, the loading machine being disposed between the seam face and the conveyor and being driven by drive means to carry out a to and fro motion along said conveyor section, said apparatus comprising first and second position indicating means responsive to the longitudinal motions of said loading and mining machines respectively for producing first and second quantities, a difference counting means responsive to said first and second position indicating means for continuously computing the difference between said first and second quantities and producing first and second control signals when the computed difference values coincide with first and second reference quantities respectively, said reference quantities corresponding respectively to predetermined maximum and minimum distances between the loading and mining machines, and switching means responsive to said first and second control signals for changing the operating condition of said drive means to limit the motion of said loading machine between said predetermined maximum and minimum distances.

6. Apparatus for controlling the operation of a loading machine that receives minerals mined by a mining machine advancing in front of the loading machine along a mineral seam and delivers the mined minerals to a conveyor the sections of which following the mining machine are pushed gradually and sequentially toward a seam face exposed by the mining machine, the loading machine being disposed between the seam face and the conveyor and being driven by drive means to carry out a to and fro motion along said conveyor section, and the roof of the seam over the mined area being supported by a roof support structure that is advanced sequentially 9 section by section by said thrust means toward the seam face as the conveyor is being pushed toward the seam face, said apparatus comprising first and second position indicating means responsive to the longitudinal motions of said loading and mining machines respectively for producing first and second quantities, a third position indicating means for producing a third quantity responsive to the location of the hereinbefore defined terminal section of one of said conveyor and roof support structure, a first difference counting means responsive to said first and third position indicating means for continuously computing the difference `between said first and third qantities and producing a first control signal as the loading machine approaches said terminal section, a second difference counting means responsive to said first and second position indicating means for continuously computing the difference between said first and second quantities and producing a second Control signal when the last-named difference coincides with a reference quantity corresponding to a predetermined minimum distance between said loading and mining machines, and switching means responsive to said first and second control signals for changing the operating condition of said drive means to limit the motion of said loading machine between said terminal section and said minimum distance.

7. The apparatus of lclaim 6, wherein said third indicating means is responsive to the distance of said terminal section from the roadway at which the seam face terminates.

References Cited UNITED STATES PATENTS 3,320,001 5/ 1967 Allen et al. 299-1 FOREIGN PATENTS 1,174,283 7/ 1964 Germany.

1,033,847 6/ 1966 Great Britain.

ERNEST R. PURSER, Primary Examiner.