APPARATUS FOR STEERING A LONGWALL MINERAL MINING MACHINE
United States Patent 3817578
Steering apparatus for a mineral mining machine having a rotary cutter head includes a probe resiliently urged towards the mine roof so as to sense the position of the cutting horizon with the mineral seam and apparatus for sensing the height of the probe with respect to the cutter head.
US Patent References:
APPARATUS FOR STEERING A LONGWALL MINERAL MINING MACHINE
Hartley - March 1973 - 3719394
APPARATUS FOR STEERING A LONGWALL MINERAL MINING MACHINE
Hartley - March 1973 - 3719394
Application Number:
05/298267
Publication Date:
06/18/1974
Filing Date:
10/17/1972
View Patent Images:
Export Citation:
Assignee:
Coal, Industry
Limited (London, EN)
Limited (London, EN)
Primary Class:
International Classes:
E21C35/24; E21C35/00; E21C27/24
Field of Search:
299/1
Primary Examiner:
Purser, Ernest R.
Attorney, Agent or Firm:
Stevens, Davis, Miller & Mosher
Claims:
I claim
1. Apparatus for steering a mineral mining machine having at least one cutter head, comprising an arm support mounting for attachment to the part of the machine carrying the cutter head for movement with said part of the machine, an arm supported by the arm support mounting, a probe carried by the arm for sensing the position of a rock boundary of a mineral seam, the probe deriving a first signal indicative of the sensed position of the rock boundary of the mineral seam, the arm being supported such that in operation the probe is urged towards said boundary, means sensing the displacement of the probe relative to the mounting, said sensing means deriving a second signal indicative of the displacement of the probe relative to the mounting, and control means arranged to receive said first and second signals and to control the machine's steering in accordance with the received signals.
2. Apparatus as claimed in claim 1, comprising inclinometer means arranged to sense the inclination of the machine and to derive a third signal indicative of the sensed inclination, the control means being arranged to receive the third signal and to control the machine's steering in accordance with the received signals.
3. Apparatus as claimed in claim 1 in which the arm comprises a hydraulic ram and the length of the arm can be varied.
4. Apparatus as claimed in claim 1 in which the arm is rigid and the arm support mounting resiliently urges the probe towards said rock boundary.
5. Apparatus for steering a mineral mining machine having at least one cutter head, comprising an arm support mounting for attachment to the part of the machine carrying the cutter head for movement with said part of the machine, a telescopic arm supported by the arm support mounting, a probe carried by the telescopic arm, the probe sensing the position of a rock boundary of a mineral seam and deriving a first signal indicative of the sensed position of the rock boundary, the telescopic arm being arranged such that in operation the probe is urged towards said rock boundary, potentiometer means sensing the length of the arm and deriving a second signal indicative of the length of the arm, and control means arranged to receive said first and second signals and to control the machine's steering in accordance with the received signals.
6. A mineral mining machine including a cutter head and steering apparatus, the steering apparatus comprising an arm support mounting for attachment to the part of the machine carrying the cutter head for movement with said part of the machine, an arm supported by the arm support mounting, a probe carried by the arm for sensing the position of a rock boundary of a mineral seam and deriving a first signal indicative of the sensed position of the rock boundary, means sensing the displacement of the probe relative to the arm support mounting and deriving a second signal indicative of the displacement of the probe relative to the arm support mounting, and control means arranged to receive said first and second signals and to control the machine's steering in accordance with the received signals.
7. A mineral mining machine as claimed in claim 6 comprising a rotary cutter head and guide means for engaging a track upon which the machine travels, the guide means being mounted directly beneath the axis of rotation of the cutter head.
1. Apparatus for steering a mineral mining machine having at least one cutter head, comprising an arm support mounting for attachment to the part of the machine carrying the cutter head for movement with said part of the machine, an arm supported by the arm support mounting, a probe carried by the arm for sensing the position of a rock boundary of a mineral seam, the probe deriving a first signal indicative of the sensed position of the rock boundary of the mineral seam, the arm being supported such that in operation the probe is urged towards said boundary, means sensing the displacement of the probe relative to the mounting, said sensing means deriving a second signal indicative of the displacement of the probe relative to the mounting, and control means arranged to receive said first and second signals and to control the machine's steering in accordance with the received signals.
2. Apparatus as claimed in claim 1, comprising inclinometer means arranged to sense the inclination of the machine and to derive a third signal indicative of the sensed inclination, the control means being arranged to receive the third signal and to control the machine's steering in accordance with the received signals.
3. Apparatus as claimed in claim 1 in which the arm comprises a hydraulic ram and the length of the arm can be varied.
4. Apparatus as claimed in claim 1 in which the arm is rigid and the arm support mounting resiliently urges the probe towards said rock boundary.
5. Apparatus for steering a mineral mining machine having at least one cutter head, comprising an arm support mounting for attachment to the part of the machine carrying the cutter head for movement with said part of the machine, a telescopic arm supported by the arm support mounting, a probe carried by the telescopic arm, the probe sensing the position of a rock boundary of a mineral seam and deriving a first signal indicative of the sensed position of the rock boundary, the telescopic arm being arranged such that in operation the probe is urged towards said rock boundary, potentiometer means sensing the length of the arm and deriving a second signal indicative of the length of the arm, and control means arranged to receive said first and second signals and to control the machine's steering in accordance with the received signals.
6. A mineral mining machine including a cutter head and steering apparatus, the steering apparatus comprising an arm support mounting for attachment to the part of the machine carrying the cutter head for movement with said part of the machine, an arm supported by the arm support mounting, a probe carried by the arm for sensing the position of a rock boundary of a mineral seam and deriving a first signal indicative of the sensed position of the rock boundary, means sensing the displacement of the probe relative to the arm support mounting and deriving a second signal indicative of the displacement of the probe relative to the arm support mounting, and control means arranged to receive said first and second signals and to control the machine's steering in accordance with the received signals.
7. A mineral mining machine as claimed in claim 6 comprising a rotary cutter head and guide means for engaging a track upon which the machine travels, the guide means being mounted directly beneath the axis of rotation of the cutter head.
Description:
This invention relates to apparatus for steering longwall mineral mining machines.
In particular the invention relates to apparatus for steering a longwall mining machine comprising a probe sensitive to the position of the machine in the mineral seam.
It is known for such apparatus to comprise a combined radiation emitter and detector probe mounted on an arm extending from the body of the longwall coal mining machine to a position adjacent to the roof boundary of the seam cut by a cutter head of the machine. As it is not practically possible for the probe to be in the actual cutting zone it must be mounted at some distance remote from the cutter head. If the probe is mounted behind the cutter head it cannot immediately sense the cutting horizon currently being cut but must wait until the machine has advanced along its path. Thus if the cutting horizon of the cutter head relative to the seam should change as it would, for example, if a conveyor pan constituting the machine track in well known manner, was inclined relative to the floor of the seam, the probe comprising the known apparatus would not detect the change until the machine had advanced sufficiently for the probe to reach the point at which the change in horizon occurred. Upon the probe reaching this point the signal from the probe would actuate the machine's steering mechanism to apply a suitable correction to the cutting horizon. By this time, however, the new cutting horizon may be still further away from its desired path within the coal seam. Alternatively by the time the probe detects the change in the cutting horizon the cutter head may be moved back to its desired path so that when the intended correction to the steering mechanism is made the cutter head is moved away from its desired path. Thus the cutter head would be caused to oscillate about the desired path repeatedly cutting the rock strata adjacent to the roof and floor of the seam.
When the strip of coal has been won and the conveyor pans are advanced towards the freshly cut face they tend to follow the undulations cut by the cutter head so that when the machine next travels along the pans the effect is accumulative and the undulations in the cutting horizon become more pronounced and may require the machine to be manually steered until a new cutting horizon is formed.
An object of the present invention is to provide apparatus for steering a longwall coal mining machine which senses changes in the cutting horizon of the machine's cutter head substantially when they occur.
According to one aspect of the present invention apparatus for steering a mineral mining machine having at least one cutter head, comprises an arm support mounting for attachment to the part of the machine carrying the cutter head for movement with such part of the machine, an arm supported by the arm support mounting, a probe carried by the arm for sensing the position of a rock boundary of the mineral seam, the arm being supported such that in operation the probe is urged towards the boundary, and means sensing the displacement of the probe relative to the mounting.
Advantageously, the length of the arm can be varied, in which case the arm may comprise a hydraulic ram.
Alternatively the arm may be rigid, in which case the arm support mounting may resiliently urge the probe towards the boundary.
Preferably, the means comprises a linear potentiometer.
Alternatively, the means comprises a rotary potentiometer.
According to another aspect of the present invention apparatus as defined above is provided in combination with the mineral mining machine.
Preferably the machine has a rotary cutter head and guide means for engaging a track upon which the machine travels, the guide means being mounted directly beneath the axis of rotation of the cutter head.
By way of example only, two embodiments of the present invention will be described with reference to the accompanying drawings, in which:
FIG. 1 is a diagrammatic side view of a longwall coal mining machine provided with a first embodiment of apparatus for steering the machine constructed in accordance with the present invention;
FIG. 2 is a diagrammatic plan of FIG. 1;
FIG. 3 is an electrical circuit diagram for the apparatus;
FIG. 4 is a diagrammatic side view of a longwall coal mining machine provided with a second embodiment of apparatus for steering the machine constructed in accordance with the present invention; and
FIG. 5 is a diagrammatic rear view of FIG. 4.
Referring to FIGS. 1 and 2, a longwall coal mining machine 1 is shown traversing along a coal face 2 along a track provided by a series of conveyor pans 3. The machine 1 has an underframe 4 and guides 5 (only one of which is shown) which engage the upper flanges of the conveyor pans 3 in a well known manner. As the machine 1 traverses along the face 2 a rotary cutter head 6 having cutter tools (not shown) wins coal from the face which is loaded onto the conveyor by means of a loading cowl (not shown) mounted behind the cutter head 6. The roof-surface of coal cut by the cutter head is shown at 7 and the floor-surface of coal is shown at 8. The guides 5 at the end of the machine adjacent to the cutter head 6 are mounted directly beneath the axis of the cutter head.
A combined radiation emitter and detector probe 10 is mounted on one end of an arm 11 which comprises an upright hydraulic ram and which is rigidly mounted in an arm support mounting 12 mounted on the machine underframe 4 for movement with the machine. The probe 10 is urged by the arm so as to contact the roof-surface 7 cut by the cutter head 6 and senses the thickness of the coal layer 13 left by the cutter head 6 below a rock boundary 14. The probe 10 emits an electric signal of typically 0.166 volts per inch thickness of coal in the layer which is fed to control means (not shown in FIGS. 1 and 2) which control the machine's steering mechanism so that the thickness of the coal layer 13 is kept within preselected limits, as for example between 4 and 5 inches. If the signal from the probe 10 indicates that the coal thickness is outside these limits the control means actuates the steering mechanism which adjusts the cutting horizon of the cutter head until the thickness of the layer is within the limits.
The machine's steering mechanism comprises hydraulic rams (not shown) interconnecting two pivotally connected parts of the underframe 4; actuation of these rams by the control means raises or lowers that part of the underframe on which the machine and arm support mounting 12 are supported relative to the other part which is attached to the guides 5.
FIG. 3 shows a part of the electrical circuit of the machine control means and, except for the probe 10 and a linear potentiometer 20 which is mounted in the arm 11, is mounted in a control panel on the body of the machine 1.
The linear potentiometer 20 is mounted in the arm 11 such that as the piston of the associated hydraulic ram is moved within the cylinder the pointer 21 passes along the two resistors of the linear potentiometer 20 with the output signal typically varying between + 10 Volts to 0 - 10 Volts depending upon the extension of the hydraulic ram. The linear potentiometer 20 typically derives an output signal of 0.166 volts per inch of change of length of the ram.
In addition to the output signals from the probe 10 and the linear potentiometer 20 the control means can receive an output signal from an inclinometer 25 mounted on the body of the machine 1 and arranged to detect the tilt of the machine relative to the mean inclination of the seam floor in a direction normal to the face 2. The output signal from the inclinometer 25 is typically 1 Volt per degree. The control means includes in the line from the inclinometer 25 a bridge network of diodes 26 which ensures that only output signals from the inclinometer 25 of greater than ± 4.3 Volts are received by the remainder of the control means. This network allows the machine 1 to tilt in a direction normal to the face within a range ± 4.3° about the mean inclination of the seam without any corrective action being taken by the control means.
The control means also receives an output signal of typically between 0 and 10 Volts from a variable resistor 28. The resistor 28 is set by the machine operator so as to give an output signal corresponding to a preselected thickness of the coal layer 13 which it is desired to leave beneath the rock boundary 14. The resistor 28 is normally locked in the set position and is only adjusted when it is desired to alter the thickness of coal layer 13.
The output signals from the probe 10, the linear potentiometer 20 and the variable resistor 28 are fed through 10,000 ohm resistors, respectively and the output signal from the inclinometer 25 is fed through a 1,000 ohm resistor. This ensures that when a signal from the inclinometer 25 is large enough to be passed through the diode arrangement 26 its effect on the control means is ten times as great as the other mentioned output signals.
All four output signals together with a negative feedback signal passing through a 10,000 ohm resistance are then fed to an inverted operational amplifier 30. As well as amplifying the signal, the amplifier 30 effectively algebraically sums the four input signals (or five if the signal from the inclinometer 25 is greater than ± 4.3 Volts) and an output signal is derived from the amplifier 30 which indicates the required position of the rams of the steering mechanism for the desired cutting horizon of the cutter head 6 to be achieved.
This signal is then passed through a 10,000 ohm resistor before being fed to a second inverted sign operational amplifier 31 acting as a comparator. The signal being fed to the amplifier 31, jointly with a negative feed-back signal and an output signal from a transducer 32 which senses the actual position of the jacks constituting the machine steering mechanism, are passed through 10,000 ohm resistors so that they have the same proportioned effect on the amplifier 31.
The amplifier 31 effectively compares the actual position of the steering mechanism with the desired or required position indicated by the output signal from the amplifier 30 and derives an output signal indicative of the error in the position of the steering mechanism. This output signal is passed through a `dead-band` circuit 33 which blocks the output signal if it falls within acceptable limits in which case the present cutting horizon of the cutter head 6 is acceptable.
If, however, the output signal from the amplifier 31 is beyond the acceptable limits it is fed by the `dead-band` circuit 33 to a control circuit 34 which suitably actuates the control valves of the steering rams until the cutting horizon of the cutter head 6 reaches an acceptable path.
In operation as the machine cuts its way along the face the output signals from the probe 10, inclinometer 25 and linear potentiometer 20 are fed to the control means.
The signal from the probe 10 maintains the thickness of the coal layer 13 within the four to five inches. If the cutting horizon of the cutter head 6 should change or if the horizon of the rock boundary 14 should vary the resulting change in the output signal from the probe 10 causes the control means to suitably adjust the steering mechanism of the machine.
If the machine tilts in a direction normal to the face beyond the acceptable ± 4.3°, the output signal from the inclinometer 25 causes the control means to re-adjust the machine's steering mechanism to correct the tilt. Since the output signal from the inclinometer is passed through a resistor which is ten times less than the 10,000 ohm resistors through which the other output signals are passed, the effect of this output signal will have markedly more effect on the control means and will effectively override the effect of the other output signals.
The output signal from the linear potentiometer 20 is indicative of the hydraulic ram or arm 11 extension. When the machine is initially set up on the face, the linear potentiometer 20 is set with the pointer 21 at the center zero position and the variable resistor 28 adjusted to give an output signal corresponding to the desired thickness of the coal layer 13. As the machine moves along its path along the face 2 any variation in the length of the arm, i.e., the vertical displacement of the probe 10 relative to the arm support mounting 12, will result in a corresponding change in the output signal from the linear potentiometer 20.
Thus if as the machine moves along the face it comes to an inclined conveyor pan 3 as shown in FIG. 1, the leading part of the machine travels up the inclined track. However, as the cutter head 6 is adjacent to the rear of the machine with its axis mounted directly above the rear guides 5 about which the machine effectively pivots during the upward movement of the leading part of the machine, the cutting horizon of cutter head 6 substantially remains unchanged.
Upon the rear guides 5 reaching the inclined pan 3 and starting to climb the incline the arm 11 is caused to contract i.e., the piston of the associated ram is pushed further into the cylinder. The reduction in length of the ram is sensed by the linear potentiometer 20 by movement of the pointer 21 along one of the resistors. The change in the output signal from the potentiometer 20 causes the control means to correspondingly adjust the cutting horizon of the cutter head 6 so that the roof-surface 7 cut by the cutter head 6 remains substantially parallel to the rock boundary 14 and the thickness of the coal layer 13 remains substantially constant.
The broken line 7' indicates the roof-surface which would have been cut by a machine having steering apparatus not provided with the present invention, the cutting horizon then being parallel to the machine track.
A similar procedure is followed if the machine should pass down an incline or over an undulation in the track.
Referring now to FIGS. 4 and 5 these show the second embodiment of apparatus for steering a longwall coal mining machine. The machine is of a similar type to that described with reference to the first embodiment of apparatus and the same reference numerals are used in FIGS. 4 and 5 for similar parts to those used in FIGS. 1 and 2.
With this second embodiment the probe 10 is mounted directly over the axis of rotation of the rotary cutter head 6 and is urged into contact with the roof of the previously won strip of coal, i.e., the roof formed during the machine's previous cutting traverse. The probe 10 is carried on an arm 11 which comprises an upright hydraulic ram and which is rigidly mounted in an arm support mounting 12 provided on the machine body 1.
If as the machine traverses the face the conveyor 3 is raised from the floor 8 as would be the case if, for example, the conveyor climbed onto a pile of fine coal deposited on the floor 8 so as to form a false floor 8', the machine would follow the conveyor and the cutter head 6 would tend to cut into the roof. The broken line 7' indicates the roof-surface which would have been cut if no steering correction had been made. However as soon as the machine body starts to lift the arm 11 senses its movement relative to the mine roof of the previously taken cut and an indicative signal is fed to control means which may be similar to those described previously with reference to the first embodiment of the invention and which correspondingly adjust the cutting horizon of the cutter head 6 so that the roof-surface 7 cut by the cutter head remains substantially parallel to the rock boundary 14 and the thickness of the coal layer 13 remains substantially constant.
It can be seen from the above description that the invention provides simple and effective apparatus for steering a longwall mineral mining machine which senses erroneous or unwanted changes in the cutting horizon of the machine's cutter head substantially when they occur and thereby virtually eliminates or minimizes such changes.
In an alternative embodiment of the invention the arm support mounting is mounted on the machine body so that the arm 11 is inclined.
In other embodiments the arm support mounting or the arm is pivotally mounted relative to the machine body and instead of the change in the arm extension being measured, the change in the inclination of the arm relative to the machine body or to the seam is determined.
In particular the invention relates to apparatus for steering a longwall mining machine comprising a probe sensitive to the position of the machine in the mineral seam.
It is known for such apparatus to comprise a combined radiation emitter and detector probe mounted on an arm extending from the body of the longwall coal mining machine to a position adjacent to the roof boundary of the seam cut by a cutter head of the machine. As it is not practically possible for the probe to be in the actual cutting zone it must be mounted at some distance remote from the cutter head. If the probe is mounted behind the cutter head it cannot immediately sense the cutting horizon currently being cut but must wait until the machine has advanced along its path. Thus if the cutting horizon of the cutter head relative to the seam should change as it would, for example, if a conveyor pan constituting the machine track in well known manner, was inclined relative to the floor of the seam, the probe comprising the known apparatus would not detect the change until the machine had advanced sufficiently for the probe to reach the point at which the change in horizon occurred. Upon the probe reaching this point the signal from the probe would actuate the machine's steering mechanism to apply a suitable correction to the cutting horizon. By this time, however, the new cutting horizon may be still further away from its desired path within the coal seam. Alternatively by the time the probe detects the change in the cutting horizon the cutter head may be moved back to its desired path so that when the intended correction to the steering mechanism is made the cutter head is moved away from its desired path. Thus the cutter head would be caused to oscillate about the desired path repeatedly cutting the rock strata adjacent to the roof and floor of the seam.
When the strip of coal has been won and the conveyor pans are advanced towards the freshly cut face they tend to follow the undulations cut by the cutter head so that when the machine next travels along the pans the effect is accumulative and the undulations in the cutting horizon become more pronounced and may require the machine to be manually steered until a new cutting horizon is formed.
An object of the present invention is to provide apparatus for steering a longwall coal mining machine which senses changes in the cutting horizon of the machine's cutter head substantially when they occur.
According to one aspect of the present invention apparatus for steering a mineral mining machine having at least one cutter head, comprises an arm support mounting for attachment to the part of the machine carrying the cutter head for movement with such part of the machine, an arm supported by the arm support mounting, a probe carried by the arm for sensing the position of a rock boundary of the mineral seam, the arm being supported such that in operation the probe is urged towards the boundary, and means sensing the displacement of the probe relative to the mounting.
Advantageously, the length of the arm can be varied, in which case the arm may comprise a hydraulic ram.
Alternatively the arm may be rigid, in which case the arm support mounting may resiliently urge the probe towards the boundary.
Preferably, the means comprises a linear potentiometer.
Alternatively, the means comprises a rotary potentiometer.
According to another aspect of the present invention apparatus as defined above is provided in combination with the mineral mining machine.
Preferably the machine has a rotary cutter head and guide means for engaging a track upon which the machine travels, the guide means being mounted directly beneath the axis of rotation of the cutter head.
By way of example only, two embodiments of the present invention will be described with reference to the accompanying drawings, in which:
FIG. 1 is a diagrammatic side view of a longwall coal mining machine provided with a first embodiment of apparatus for steering the machine constructed in accordance with the present invention;
FIG. 2 is a diagrammatic plan of FIG. 1;
FIG. 3 is an electrical circuit diagram for the apparatus;
FIG. 4 is a diagrammatic side view of a longwall coal mining machine provided with a second embodiment of apparatus for steering the machine constructed in accordance with the present invention; and
FIG. 5 is a diagrammatic rear view of FIG. 4.
Referring to FIGS. 1 and 2, a longwall coal mining machine 1 is shown traversing along a coal face 2 along a track provided by a series of conveyor pans 3. The machine 1 has an underframe 4 and guides 5 (only one of which is shown) which engage the upper flanges of the conveyor pans 3 in a well known manner. As the machine 1 traverses along the face 2 a rotary cutter head 6 having cutter tools (not shown) wins coal from the face which is loaded onto the conveyor by means of a loading cowl (not shown) mounted behind the cutter head 6. The roof-surface of coal cut by the cutter head is shown at 7 and the floor-surface of coal is shown at 8. The guides 5 at the end of the machine adjacent to the cutter head 6 are mounted directly beneath the axis of the cutter head.
A combined radiation emitter and detector probe 10 is mounted on one end of an arm 11 which comprises an upright hydraulic ram and which is rigidly mounted in an arm support mounting 12 mounted on the machine underframe 4 for movement with the machine. The probe 10 is urged by the arm so as to contact the roof-surface 7 cut by the cutter head 6 and senses the thickness of the coal layer 13 left by the cutter head 6 below a rock boundary 14. The probe 10 emits an electric signal of typically 0.166 volts per inch thickness of coal in the layer which is fed to control means (not shown in FIGS. 1 and 2) which control the machine's steering mechanism so that the thickness of the coal layer 13 is kept within preselected limits, as for example between 4 and 5 inches. If the signal from the probe 10 indicates that the coal thickness is outside these limits the control means actuates the steering mechanism which adjusts the cutting horizon of the cutter head until the thickness of the layer is within the limits.
The machine's steering mechanism comprises hydraulic rams (not shown) interconnecting two pivotally connected parts of the underframe 4; actuation of these rams by the control means raises or lowers that part of the underframe on which the machine and arm support mounting 12 are supported relative to the other part which is attached to the guides 5.
FIG. 3 shows a part of the electrical circuit of the machine control means and, except for the probe 10 and a linear potentiometer 20 which is mounted in the arm 11, is mounted in a control panel on the body of the machine 1.
The linear potentiometer 20 is mounted in the arm 11 such that as the piston of the associated hydraulic ram is moved within the cylinder the pointer 21 passes along the two resistors of the linear potentiometer 20 with the output signal typically varying between + 10 Volts to 0 - 10 Volts depending upon the extension of the hydraulic ram. The linear potentiometer 20 typically derives an output signal of 0.166 volts per inch of change of length of the ram.
In addition to the output signals from the probe 10 and the linear potentiometer 20 the control means can receive an output signal from an inclinometer 25 mounted on the body of the machine 1 and arranged to detect the tilt of the machine relative to the mean inclination of the seam floor in a direction normal to the face 2. The output signal from the inclinometer 25 is typically 1 Volt per degree. The control means includes in the line from the inclinometer 25 a bridge network of diodes 26 which ensures that only output signals from the inclinometer 25 of greater than ± 4.3 Volts are received by the remainder of the control means. This network allows the machine 1 to tilt in a direction normal to the face within a range ± 4.3° about the mean inclination of the seam without any corrective action being taken by the control means.
The control means also receives an output signal of typically between 0 and 10 Volts from a variable resistor 28. The resistor 28 is set by the machine operator so as to give an output signal corresponding to a preselected thickness of the coal layer 13 which it is desired to leave beneath the rock boundary 14. The resistor 28 is normally locked in the set position and is only adjusted when it is desired to alter the thickness of coal layer 13.
The output signals from the probe 10, the linear potentiometer 20 and the variable resistor 28 are fed through 10,000 ohm resistors, respectively and the output signal from the inclinometer 25 is fed through a 1,000 ohm resistor. This ensures that when a signal from the inclinometer 25 is large enough to be passed through the diode arrangement 26 its effect on the control means is ten times as great as the other mentioned output signals.
All four output signals together with a negative feedback signal passing through a 10,000 ohm resistance are then fed to an inverted operational amplifier 30. As well as amplifying the signal, the amplifier 30 effectively algebraically sums the four input signals (or five if the signal from the inclinometer 25 is greater than ± 4.3 Volts) and an output signal is derived from the amplifier 30 which indicates the required position of the rams of the steering mechanism for the desired cutting horizon of the cutter head 6 to be achieved.
This signal is then passed through a 10,000 ohm resistor before being fed to a second inverted sign operational amplifier 31 acting as a comparator. The signal being fed to the amplifier 31, jointly with a negative feed-back signal and an output signal from a transducer 32 which senses the actual position of the jacks constituting the machine steering mechanism, are passed through 10,000 ohm resistors so that they have the same proportioned effect on the amplifier 31.
The amplifier 31 effectively compares the actual position of the steering mechanism with the desired or required position indicated by the output signal from the amplifier 30 and derives an output signal indicative of the error in the position of the steering mechanism. This output signal is passed through a `dead-band` circuit 33 which blocks the output signal if it falls within acceptable limits in which case the present cutting horizon of the cutter head 6 is acceptable.
If, however, the output signal from the amplifier 31 is beyond the acceptable limits it is fed by the `dead-band` circuit 33 to a control circuit 34 which suitably actuates the control valves of the steering rams until the cutting horizon of the cutter head 6 reaches an acceptable path.
In operation as the machine cuts its way along the face the output signals from the probe 10, inclinometer 25 and linear potentiometer 20 are fed to the control means.
The signal from the probe 10 maintains the thickness of the coal layer 13 within the four to five inches. If the cutting horizon of the cutter head 6 should change or if the horizon of the rock boundary 14 should vary the resulting change in the output signal from the probe 10 causes the control means to suitably adjust the steering mechanism of the machine.
If the machine tilts in a direction normal to the face beyond the acceptable ± 4.3°, the output signal from the inclinometer 25 causes the control means to re-adjust the machine's steering mechanism to correct the tilt. Since the output signal from the inclinometer is passed through a resistor which is ten times less than the 10,000 ohm resistors through which the other output signals are passed, the effect of this output signal will have markedly more effect on the control means and will effectively override the effect of the other output signals.
The output signal from the linear potentiometer 20 is indicative of the hydraulic ram or arm 11 extension. When the machine is initially set up on the face, the linear potentiometer 20 is set with the pointer 21 at the center zero position and the variable resistor 28 adjusted to give an output signal corresponding to the desired thickness of the coal layer 13. As the machine moves along its path along the face 2 any variation in the length of the arm, i.e., the vertical displacement of the probe 10 relative to the arm support mounting 12, will result in a corresponding change in the output signal from the linear potentiometer 20.
Thus if as the machine moves along the face it comes to an inclined conveyor pan 3 as shown in FIG. 1, the leading part of the machine travels up the inclined track. However, as the cutter head 6 is adjacent to the rear of the machine with its axis mounted directly above the rear guides 5 about which the machine effectively pivots during the upward movement of the leading part of the machine, the cutting horizon of cutter head 6 substantially remains unchanged.
Upon the rear guides 5 reaching the inclined pan 3 and starting to climb the incline the arm 11 is caused to contract i.e., the piston of the associated ram is pushed further into the cylinder. The reduction in length of the ram is sensed by the linear potentiometer 20 by movement of the pointer 21 along one of the resistors. The change in the output signal from the potentiometer 20 causes the control means to correspondingly adjust the cutting horizon of the cutter head 6 so that the roof-surface 7 cut by the cutter head 6 remains substantially parallel to the rock boundary 14 and the thickness of the coal layer 13 remains substantially constant.
The broken line 7' indicates the roof-surface which would have been cut by a machine having steering apparatus not provided with the present invention, the cutting horizon then being parallel to the machine track.
A similar procedure is followed if the machine should pass down an incline or over an undulation in the track.
Referring now to FIGS. 4 and 5 these show the second embodiment of apparatus for steering a longwall coal mining machine. The machine is of a similar type to that described with reference to the first embodiment of apparatus and the same reference numerals are used in FIGS. 4 and 5 for similar parts to those used in FIGS. 1 and 2.
With this second embodiment the probe 10 is mounted directly over the axis of rotation of the rotary cutter head 6 and is urged into contact with the roof of the previously won strip of coal, i.e., the roof formed during the machine's previous cutting traverse. The probe 10 is carried on an arm 11 which comprises an upright hydraulic ram and which is rigidly mounted in an arm support mounting 12 provided on the machine body 1.
If as the machine traverses the face the conveyor 3 is raised from the floor 8 as would be the case if, for example, the conveyor climbed onto a pile of fine coal deposited on the floor 8 so as to form a false floor 8', the machine would follow the conveyor and the cutter head 6 would tend to cut into the roof. The broken line 7' indicates the roof-surface which would have been cut if no steering correction had been made. However as soon as the machine body starts to lift the arm 11 senses its movement relative to the mine roof of the previously taken cut and an indicative signal is fed to control means which may be similar to those described previously with reference to the first embodiment of the invention and which correspondingly adjust the cutting horizon of the cutter head 6 so that the roof-surface 7 cut by the cutter head remains substantially parallel to the rock boundary 14 and the thickness of the coal layer 13 remains substantially constant.
It can be seen from the above description that the invention provides simple and effective apparatus for steering a longwall mineral mining machine which senses erroneous or unwanted changes in the cutting horizon of the machine's cutter head substantially when they occur and thereby virtually eliminates or minimizes such changes.
In an alternative embodiment of the invention the arm support mounting is mounted on the machine body so that the arm 11 is inclined.
In other embodiments the arm support mounting or the arm is pivotally mounted relative to the machine body and instead of the change in the arm extension being measured, the change in the inclination of the arm relative to the machine body or to the seam is determined.