Patent Publication Number: US-10316659-B2

Title: Stabilization system for a mining machine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of prior-filed, co-pending U.S. patent application Ser. No. 15/588,193, filed May 5, 2017, which is a continuation of U.S. patent application Ser. No. 14/630,172, filed Feb. 24, 2015, which is a continuation of U.S. patent application Ser. No. 13/566,150, filed Aug. 3, 2012, which claims the benefit of prior-filed, U.S. Provisional Application No. 61/514,542, filed Aug. 3, 2011, U.S. Provisional Patent Application No. 61/514,543, filed Aug. 3, 2011, and U.S. Provisional Patent Application No. 61/514,566, filed Aug. 3, 2011, the entire contents of all of which are hereby incorporated by reference. The present application also incorporates by reference the entire contents of PCT Patent Application No. PCT/US2012/049532, filed Aug. 3, 2012, and U.S. Non-Provisional patent application Ser. No. 13/566,462, filed Aug. 3, 2012. 
    
    
     BACKGROUND 
     The present invention relates to mining equipment, and particularly to continuous mining machines. 
     Traditionally, excavation of hard rock in the mining and construction industries, has generally taken one of two forms, explosive excavation or rolling edge disc cutter excavation. Explosive mining entails drilling a pattern of holes of relatively small diameter into the rock being excavated, and loading those holes with explosives. The explosives are then detonated in a sequence designed to fragment the required volume of rock for subsequent removal by suitable loading and transport equipment. However, the relatively unpredictable size distribution of the rock product formed complicates downstream processing. 
     Mechanical fragmentation of rock eliminates the use of explosives; however, rolling edge cutters require the application of very large forces to crush and fragment the rock under excavation. Conventional underground mining operations may cause the mine roof (also called the hanging wall) and mine walls to become unstable. In order to prevent the walls from collapsing as the mining machine bores deeper into a mineral seam, hydraulic cylinders are used to support the mine walls. To support the hanging wall, the hydraulic cylinders often must exert forces of over 40 tons against the hanging wall. This force causes the hydraulic support to bore into the hanging wall, which weakens the hanging wall and increases the risk of falling rocks. 
     SUMMARY 
     One embodiment provides a mining machine including a frame, a cutting head moveably coupled to the frame and pivotable about an axis that is substantially perpendicular to a first mine surface, and a first actuator for stabilizing the frame relative to the first mine surface. The first actuator is coupled to the frame and includes a first end extendable in a first direction to engage the first mine surface. The extension of the first actuator is automatically controlled based on measurements of at least one indicator of the force between the first actuator and the first mine surface. 
     Another embodiment provides a method for stabilizing a mining machine relative to a mine surface. The method includes extending at least one actuator toward a mine surface until at least one indicator of the force between the actuator and the mine surface reaches a predetermined value, retracting the at least one actuator for a predetermined amount of time, and extending the at least one actuator for the predetermined amount of time plus an additional amount of time. 
     Yet another embodiment provides a method for stabilizing a mining machine relative to a first mine surface and a second mine surface. The method includes extending a first actuator toward the first mine surface until at least one indicator of the force between the first actuator and the first mine surface reaches a predetermined value, retracting the first actuator by a first predetermined distance, extending the first actuator by the first predetermined distance plus an offset distance, extending a second actuator toward the second mine surface until at least one indicator of the force between the second actuator and the second mine surface reaches a predetermined value, retracting the second actuator by a second predetermined distance, and extending the second actuator by the second predetermined distance plus an offset distance. 
     In some embodiments, a mining machine includes a frame, a cutting head supported for movement on the frame, an actuator for stabilizing the frame relative to a mine surface, and a control system configured to operate the actuator. The actuator is coupled to the frame and includes an end extendable in a first direction to engage the mine surface. The control system is configured to retract the actuator, for a predetermined amount of time, from a position at which at least one indicator of the force between the actuator and the mine surface satisfies a specified range, and extend the actuator for the predetermined amount of time plus an additional amount of time. 
     In some embodiments, a control system for operating at least one stabilization member to engage a support surface includes a sensor and a controller in communication with the sensor. The sensor is configured to detect at least one indicator of a force exerted between an end of the stabilization member and the support surface. The controller is configured to retract the stabilization member, for a predetermined amount of time, from a position at which the at least one indicator of the force between the stabilization member and the support surface satisfies a specified range. The controller is further configured to extend the stabilization member for the predetermined amount of time plus an additional amount of time. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a mining machine. 
         FIG. 2  is a side view of the mining machine of  FIG. 1 . 
         FIG. 3  is a perspective view of a cutting mechanism. 
         FIG. 4  is an exploded perspective view of the cutting mechanism of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of a cutter head of the cutting mechanism of  FIG. 3 . 
         FIG. 6  is a perspective view of a stabilizer in a retracted state. 
         FIG. 7  is a perspective view of the stabilizer of  FIG. 6  in an extended state. 
         FIG. 8  is a cross-section view of the stabilizer of  FIG. 6  taken along line  8 - 8 . 
         FIG. 9  is a side view of a headboard. 
         FIG. 10  is a perspective view of a headboard. 
         FIG. 11  is a cross-sectional view of the headboard of  FIG. 10  taken along line  11 - 11 . 
         FIG. 12  is a perspective view of a spacer. 
         FIG. 13  is a side view of a headboard and spacer in a stacked configuration. 
         FIG. 14  is a partial side view of the mining machine of  FIG. 1  with a leveling actuator in an extended state. 
         FIG. 15  is a partial side view of the mining machine of  FIG. 1  with a leveling actuator and a support actuator in extended states. 
         FIG. 16  is a partial side view of the mining machine of  FIG. 1  with a leveling actuator and a support actuator in extended states and further including a spacer positioned adjacent a headboard coupled to each actuator. 
         FIG. 17  is a schematic diagram of a hydraulic control system for a stabilizer. 
         FIG. 18  is a schematic diagram of a leveling selection sequence. 
         FIG. 19  is a schematic diagram of a leveling control sequence for automatic extension and retraction of the stabilizers. 
         FIG. 20  is a schematic diagram of a leveling control sequence for manual leveling of the stabilizers. 
         FIG. 21  is a schematic diagram of a stabilizing control sequence. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of 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. The use of “including,” “comprising” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “mounted,” “connected” and “coupled” are used broadly and encompass both direct and indirect mounting, connecting and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical or hydraulic connections or couplings, whether direct or indirect. Also, electronic communications and notifications may be performed using any known means including direct connections, wireless connections, etc. 
       FIGS. 1 and 2  show a continuous mining machine  10  including a frame  14 , a stabilization system  18 , a cutting mechanism  22  coupled to the frame  14 , and a pair of tracks  24  coupled to the frame  14 , for moving the machine  10 . Before describing the stabilization system  18 , the mining machine  10  and cutting mechanism  22  will be described in detail. 
     As shown in  FIGS. 3 and 4 , the cutting mechanism  22  includes a cutter head  26 , an arm  30  defining a longitudinal axis  34 , a bracket  42  for attaching the cutter head  26  to the arm  30 , and a pivot assembly  50  coupled to the mining machine  10  and permitting the arm  30  to be pivoted about an axis  52  ( FIG. 1 ) substantially perpendicular to a floor or surface on which the machine  10  is supported. Stated another way, the arm  30  pivots in a substantially horizontal direction. The cutter head includes a flange  54  and three openings  58  ( FIG. 4 ), each of which releasably receives a disc cutter assembly  66 . The disc cutter assemblies  66  are spaced apart from one another and oriented along separate axes. Each disc cutter assembly  66  defines a longitudinal axis of rotation  70 , and the disc cutter assemblies  66  are spaced apart from one another and mounted at an angle such that the axes of rotation  70  are not parallel and do not intersect. For instance, in the embodiment shown in  FIG. 3 , the axis  70   a  of the center disc cutter assembly  66   a  is substantially coaxial with the longitudinal axis  34  of the arm  30 . The axis  70   b  of the lower disc cutter assembly  66   b  is at an angle to the axis  70   a  of the center disc cutter  66   a . The axis  70   c  of the upper disc cutter assembly  66   c  is at an angle to the axes  70   a ,  70   b  of the center disc cutter assembly  66   a  and the lower disc cutter assembly  66   b . This arrangement of the disc cutter assemblies  66  produces even cuts when the cutter head  26  engages the mine wall. Further embodiments may include fewer or more cutting disc assemblies  66  arranged in various positions. 
     As shown in  FIG. 5 , the cutter head  26  also includes an absorption mass  74 , in the form of a heavy material, such as lead, located in an interior volume of the cutter head  26  surrounding the three openings  58 . By having the three eccentrically driven disc cutter assemblies  66  share a common heavy weight, less overall weight is necessary and permits a lighter and more compact design. In one embodiment, approximately 6 tons is shared among the three disc cutter assemblies  66 . The mounting arrangement is configured to react to the approximate average forces applied by each disc cutter assembly  66 , while peak cutting forces are absorbed by the absorption mass  74 , rather than being absorbed by the arm  30  ( FIG. 3 ) or other support structure. The mass of each disc cutter assembly  66  is relatively much smaller than the absorption mass  74 . 
     In the embodiment shown in  FIG. 4 , the arm  30  includes a top portion  82  and a bottom portion  86 . The bracket  42  includes a flange  94 . The bracket  42  is secured to the arm  30  by any suitable fashion, such as welding. The bracket  42  is attached to the cutter head  26  by U-shaped channels  98 . Each channel  98  receives the cutter head flange  54  and the bracket flange  94  to secure the cutter head  26  to the bracket  42 . A resilient sleeve (not shown) is placed between the cutter head  26  and the bracket  42  to isolate cutter head vibrations from the arm  30 . 
     The disc cutter assemblies  66  are driven to move in an eccentric manner. This is accomplished, for instance, by driving the disc cutter assemblies  66  using a drive shaft (not shown) having a first portion defining a first axis of rotation and a second portion defining a second axis of rotation that is radially offset from the first axis of rotation. The magnitude of eccentric movement is proportional to the amount of radial offset between the axis of rotation of each portion of the shaft. In one embodiment, the amount of offset is a few millimeters, and the disc cutter assembly  66  is driven eccentrically through a relatively small amplitude at a high frequency, such as approximately 3000 RPM. 
     The eccentric movement of the disc cutter assemblies  66  creates a jackhammer-like action against the mineral to be mined, causing tensile failure of the rock so that chips of rock are displaced from the rock surface. The force required to produce tensile failure in the rock is an order of magnitude less than that required by conventional rolling edge disc cutters to remove the same amount of rock. The action of the disc cutter assembly  66  against the under face is similar to that of a chisel in developing tensile stresses in a brittle material, such as rock, which is caused effectively to fail in tension. In another embodiment, the disc cutter  66  could also nutate such that the axis of rotation moves in a sinusoidal manner as the disc cutter  66  oscillates. This could be accomplished by making the axis about which the disc cutter drive shaft rotates angularly offset from a disc cutter housing. 
     The mining machine  10  is operated by advancing the arm  30  toward the material to be mined a first incremental distance, pivoting the arm  30  to cut the material, and then advancing the arm  30  toward the material to be mined a second incremental distance. During operation, the lower disc cutter assembly  66   b  is the first to contact the mineral to be mined when the arm  30  is pivoted in a first direction (clockwise as viewed from the top of the arm  30  in  FIG. 3 ) about the pivot assembly  50 . This results in the lower disc cutter assembly  66   b  dislodging material that falls away from the mine wall. As the center disc cutter assembly  66   a  contacts the mineral to be mined, the space below the center disc cutter assembly  66   a  has been opened by the lower disc cutter assembly  66   b , so the material dislodged by the center disc cutter assembly  66   a  falls away from the mine wall. Likewise, as the upper disc cutter assembly  66   c  engages the material, the space below the upper disc cutter assembly  66   c  is open, and the material dislodged by upper disc cutter assembly  66   c  falls to the floor. Since the leading disc cutter is in the lower most position, the material dislodged by leading disc cutters is not re-crushed by trailing disc cutter, reducing wear on the disc cutters. In addition, the disc cutter assemblies  66  are positioned so that each disc cutter  66  cuts equal depths into the material to be mined. This prevents unevenness in the mineral to be mined that could obstruct the progress of the mining machine  10 . 
     The stabilization system  18  may be used in combination with the continuous mining machine  10  described above, or may be used in combination with a mining machine as described in U.S. Pat. No. 7,934,776, filed Aug. 31, 2007, the entire contents of which are incorporated herein by reference. The stabilization system  18  provides added support against rock fall, and also insures that the cutting mechanism  22  cuts on a level plane with respect to the mine floor. 
     Referring again to  FIGS. 1 and 2 , the stabilization system  18  includes at least one stabilizer  534 . In the illustrated embodiment, the stabilization system  18  includes four stabilizers  534 , with one stabilizer  534  positioned at each of the four corners of the machine  10 . In other embodiments, the machine  10  may include fewer or more than four stabilizers  534  and may be arranged in positions other than the four corners of the machine  10 . 
     Referring to  FIGS. 6 and 7 , each stabilizer  534  includes a housing  538 , a leveling actuator  542 , a support actuator  546  independent of the leveling actuator  542 , and a headboard  550  coupled to the end of each actuator  542 ,  546 . As shown in  FIG. 8 , both the support actuator  546  and the leveling actuator  542  are mounted side-by-side within the housing  538 . The actuators  542 ,  546  include a displacement transducer  552  ( FIG. 8 ) to sense the position of each actuator  542 ,  546  within the housing  538 . The leveling actuator  542  is used to level the machine  10 , while the support actuator  546  is used in combination with the leveling actuator  542  to provide support and gripping force for the machine during the mining process. In the illustrated embodiment, the stabilizer  534  is strategically positioned relative to the machine to ensure maximum support and optimum leveling capabilities. In further embodiments (described below), each stabilizer  534  may also include one or more spacers  554  ( FIGS. 12 and 13 ). 
     In the illustrated embodiment, the actuators  542 ,  546  are double-acting type hydraulic cylinders and hydraulic pressure is selectively applied to either side of a piston  544 ,  548  ( FIG. 8 ) in order to extend or retract the cylinders. In other embodiments, the actuators  542 ,  546  can include another type of hydraulic actuator, a pneumatic actuator, an electric actuator (e.g., a switch or relay, a piezoelectric actuator, or a solenoid), a mechanical actuator (e.g., a screw or cam actuator), or another type of mechanism or system for moving a component of the mining machine. 
     As shown in  FIGS. 9-11 , the headboard  550  has a wide profile, or footprint, which provides a greater surface area of support. In the illustrated embodiment, the headboard  550  is generally triangular (with truncated corners). The headboard  550  includes a first side  558  for engaging the hanging wall (mine roof) or the footwall (mine floor), a second side  562  opposite the first side  558 , a pair of handles  566  coupled to the second side  562 , a socket  570  ( FIG. 11 ) positioned on the second side  562 , and a mounting surface  574  surrounding the socket  570 . The handles  566  are provided to assist in handling and transporting the headboard  550  for installation on the stabilizer  534 . In one embodiment, the headboard  550  is formed from a glass-reinforced plastic, and the first side  558  is bonded with a polyurethane friction material. The polyurethane material acts as a friction surface to protect the headboard  550  from damage. 
     Referring to  FIGS. 9 and 11 , the headboard  550  is coupled to each actuator  542 ,  546  ( FIG. 9 ) by a joint assembly  578 . In the illustrated embodiment, the joint assembly  578  is a ball-in-socket type coupling. As shown in  FIG. 11 , the joint assembly  578  includes a ball member  586 , a flange  590  (which may be formed from polyurethane), and a locating pin  594 . The ball member  586  includes a first end  598  having a round shape, a second end  606 , and a groove  614  extending circumferentially around the ball member  586  between the first end  598  and the second end  606 . The first end  598  fits within the headboard socket  570  to allow pivoting movement of the socket  570  about the ball member  586 . The second end  606  has a cylindrical shape and includes a longitudinal bore  618  that fits over the actuators  542 ,  546 . 
     The flange  590  of the joint assembly  578  is secured to the mounting surface  574  on the headboard  550  and is positioned within the groove  614  of the ball member  586 . This arrangement allows the ball member  586  to pivot relative to the socket  570  to some degree, but the pivoting movement of ball member  586  is limited by the flange  590 . The joint assembly  578  provides a self-aligning feature for the stabilizers  534 , such that when the actuators  542 ,  546  are extended, the headboard  550  moves with respect to the ball joint  578  in order to lie flat against the roof or floor. In addition, when the actuators  542 ,  546  are retracted away from the floor or roof, the headboard  550  maintains its horizontal position. The bore  618  of the ball member  586  is slid over an end of one of the actuators  542 ,  546  and is secured by the locating pin  594 . In this way, a headboard  550  is secured to each leveling actuator  542  and support actuator  546 . 
     The headboard  550  enhances the efficiency of the stabilizers  534 . The headboard  550  may be made of composite material rather than steel to provide reduced weight and improved handling. The headboard  550  sustains a larger load and provides coverage over a larger area than previous designs. The headboard  550  is durable and can deform elastically, which aids in withstanding shocks caused by blasting. The composite material for the headboard  550  is unreactive and corrosion-resistant. These factors give the composite headboard  550  a longer life, reducing the overall cost of the stabilizers  534 . In addition, the headboard  550  exerts a stabilizing force against the footwall as well as the roof. The headboard  550  can accommodate uneven mine roof and floor conditions through the adaptive joint assembly  578 . 
     As shown in  FIG. 12 , each spacer  554  includes a first side  622  and a web  626  opposite the first side  622 , and locating holes  630  positioned within the web  626 . The first side  622  is adapted to engage the mine roof or floor. The web  626  includes multiple plates  634  to support the necessary load. As shown in  FIG. 13 , the spacer  554  can be positioned between the headboard  550  and the mine roof or floor. In further embodiments, the spacer  554  may be coupled directly to one of the actuators  542 ,  546  by a joint assembly similar to the joint assembly  578 , and the headboard  550  is then positioned between the spacer  554  and the mine floor or roof. 
     Multiple spacers  554  may be stacked on the first side  558  of the headboard  550  to support the mine roof or floor. The locating holes  630  for each spacer  554  are aligned and a pin (not shown) is placed within the hole  630  to insure the spacers  554  remain aligned with one another in a column and do not slip. In other embodiments, the spacer  554  may not include any locating holes. In one embodiment, the spacers  554  are formed from steel and are coated with a material having a high coefficient of friction. The spacers  554  support a large load in compression and have a reduced mass for a consistent strength-to-weight ratio. The mass reduction provides easier handling and transportation. 
     In another embodiment (not shown), the stabilizers  534  include side actuators oriented in a horizontal direction to support the side walls of the mine. The stabilizers in this case would include features similar to the stabilizers  534  described above, including the headboard  550  and the joint assembly  578 . 
     As shown in  FIGS. 14-16 , the stabilizers  534  perform both the leveling and stabilization functions for the continuous mining machine  10 . First, as the mining machine  10  is positioned near the wall to be mined, both the support actuators  546  and the leveling actuators  542  are retracted ( FIG. 6 ). The leveling actuators  542  are then extended ( FIG. 14 ) in order to orient the machine  10  at an angle suitable to complete the mining operation. The headboards  550  of the leveling actuators  542  engage the mine floor. Then, to insure that the continuous mining machine  10  is stabilized during the cutting operation, the support actuators  546  are extended such that the headboards  550  engage the mine roof ( FIG. 15 ). In addition, as shown in  FIG. 16 , one or more spacers  554  may be positioned between each headboard  550  and the mine roof and mine floor. 
     The stabilizers  534  are controlled via a control system  638 , and a representative control system  638  is shown in  FIG. 17 . Although the control system  638  is described below with respect to a hydraulic system, a similar control system may be applied using any of several different types of power systems. 
     In some embodiments, the control system  638  indirectly measures the physical force between the actuators  542 ,  546  and the mine surface. In particular, parameters of the actuators  542 ,  546  can provide one or more indicators of the physical force between the actuators  542 ,  546  and the mine surface. The control system  638  can determine if these indicators equal or exceed a predetermined value to indirectly determine if the physical force between the actuators  542 ,  546  and the mine surface has reached the predetermined threshold. For example, if the actuators  542 ,  546  include hydraulic cylinders, the control system  638  can use a pressure value of the actuators  542 ,  546  as an indicator of the physical force applied between the actuators  542 ,  546  and the mine surface. In particular, the control system  638  can extend the actuators  542 ,  546  toward the mine surface until the actuators  542 ,  546  are pressurized to a predetermined pressure value. The control system  638  can use a similar pressure value as an indicator of the physical force between the actuators  542 ,  546  and the mine surface when the actuators  542 ,  546  include pneumatic actuators. In other embodiments, the control system  638  can use parameters of a current supplied to the actuators  542  and  546 , a force value between components of the actuators  542  and  546 , or a physical position of a component of the actuators  542  and  546  as the indicator of the physical force between the actuators  542 ,  546  and the mine surface. Other components of the machine  10 , such as displacement transducers or an inclinometer, can also provide one or more feedback indicators of the physical force between the actuators  542 ,  546  and the mine surface. 
     In the illustrated embodiment, the control system  638  includes a control manifold  642  mounted separately from the stabilizer housing  538 , displacement transducers  552  ( FIG. 8 ), pressure transducers  692  (shown schematically in  FIG. 17 ), an inclinometer (not shown), and a programmable logic controller (“PLC”; not shown). The displacement transducers  552  and pressure transducers  692  are mounted on the actuators  542 ,  546  and measure the actuator position and pressure, respectively, to provide feedback to the control system  638  regarding the force between the actuators  542 ,  546  and the mine surface. The inclinometer measures the inclination of the machine  10  in both longitudinal and lateral directions. In other embodiments, other sensors may be used to measure an indicator of the physical force between the actuators  542 ,  546  and the mine surface. 
     As shown in  FIG. 17 , the control manifold  642  includes a leveling system  650  and a support system  654 . The leveling system  650  includes a high-response servo solenoid valve or proportional valve  662  having onboard control electronics and a fail safe position, a pressure-reducing valve  666 , a two-position directional control valve  670 , a pilot-operated check valve  674 , and a pressure relief valve  678 . These components are associated with the leveling actuators  542 . The support system  654  includes a first permissive valve  682  for extending the support actuator  546 , a second permissive valve  686  for retracting the support actuator  546 , and pilot-operated check valves  690 . These components are associated with each support actuator  546 . The permissive valves  682  and  686  are two-position directional control valves. The support system  654  will be discussed in detail after describing the leveling system  646 . 
     The proportional valve  662  controls the direction and magnitude of oil flow into each actuator  542  by permitting precise control of oil into a full-bore side of the leveling actuators  542 . The pressure reducing valve  666  maintains a permanent connection between a rod side of the leveling actuators  542  and the main pressure supply. The pressure reducing valve  666  sets the balance pressure, which is used to retract the leveling actuators  542  and lower the mining machine  10  onto its tracks  24  when required. In one embodiment, the balance pressure is approximately 20 bar. Although the weight of the machine  10  is sufficient to lower the machine  10  when the proportional valve  662  bleeds off a precise amount of oil, the leveling actuator  542  is lifted off the floor to a retracted position before the machine  10  can tram to perform the mining operation. 
     When a desired machine position is reached, the leveling actuator  542  is locked in position by the pilot-operated check valve  674 . The two-position, three-way directional control valve  670  controls the oil flow to the proportional valve  662  and also supplies the pilot pressure to the pilot-operated check valve  674 . The directional control valve  670  is energized when any adjustment is required and is de-energized as soon as the desired position is reached. The direct-operated pressure relief valve  678  limits the downward pushing force (i.e., the lifting force) of each actuator  542 . The pressure relief valve  678  is set to an optimal pressure value to limit any pressure peaks which may occur during normal or abnormal operations. 
     The four leveling actuators  542  are capable of being controlled either individually or as a group via a remote control. For instance, to move a single leveling actuator  542 , the operator can select the respective actuator  542  on the remote control and actuate a joystick in the desired direction of movement (i.e., up or down). 
     The continuous mining machine  10  includes a logic controller (not shown) to control leveling of the machine  10 . As shown in  FIG. 18 , the logic controller includes a leveling selection sequence  700  to select between multiple leveling sequences for the leveling actuators  542 . In the illustrated embodiment, a logic controller includes an automatic extend sequence  800  ( FIG. 19 ), automatic retract sequence  900  ( FIG. 19 ), and an individual leveling sequence  1000  ( FIG. 20 ). 
     Referring to  FIG. 18 , the leveling selection sequence  700  includes the first step  710  of placing all proportional valves  662  and directional control valves  670  in the off position. The next step  720  is to place the proportional valves  662  in a neutral position, select either individual or automatic leveling, and select a direction for movement of the leveling actuators  542 . If an automatic DOWN direction is selected (step  730 ), the controller initiates the automatic extend sequence  800  ( FIG. 19 ). If an automatic UP direction is selected (step  740 ), the controller initiates the automatic retract sequence  900  ( FIG. 19 ). If any of the actuator buttons indicating individual leveling is selected then the controller initiates the individual leveling sequence  1000  if appropriate ( FIG. 20 ). In this way, leveling of the mining machine  10  is done automatically by the control system  638  in response to a controller command. In one embodiment, the operator presses a combination of buttons on a remote control together with moving the joystick in the desired direction (up or down) to initiate a command sequence to support or un-support the machine  10 . 
     When the automatic extend sequence  800  is entered, the leveling actuators  542  are actuated downwards until the indicator of the physical force between the actuators  542  and the mine surface reaches a predetermined value. Referring to  FIG. 19 , the automatic extend sequence  800  first sets the proportional valves  662  to actuate the leveling actuators  542  (step  810 ). Each leveling actuator  542  extends at a preset speed, and the system determines when each respective headboard  550  engages the mine floor by detecting when the indicator reaches a predetermined value or falls within a specified range of values (step  820 ). In the illustrated embodiment, the indicator is the pressure gradient within the leveling actuator  542 . The pressure is monitored using, for instance, a discrete first derivative of pressure measurements from a pressure transducer  692  for each leveling actuator  542 . Initial movement is ignored for a programmable period of time (step  830 ), since the pressure curve during the initial movement each actuator  542  is similar to the pressure curve exhibited when the headboard  550  engages the floor. 
     Once the leveling actuators  542  reach the mine floor, the leveling actuators  542  are stopped (step  840 ) and a delay timer starts to allow for the accurate measurement of the displacement of actuator  542  (step  850 ). If the pre-determined value of the indicator is reached outside the bounds of the maximum extension length or the maximum extension time, then the automatic extend sequence  800  is aborted. If one or more leveling actuators  542  fails to find the floor within a specified time, then extension of all stabilizers  534  is stopped and the automatic extend sequence  800  is aborted. In either case (i.e., whether all stabilizers  534  touch the floor or if any leveling actuator  542  fails), the operator receives an indication from, for instance, an indicator light or from the remote control. If a leveling actuator  542  fails to touch the floor, the operator may individually control the respective actuator  542 . 
     Once all leveling actuators  542  engage the floor, the operator is able to adjust individual leveling actuators  542  from the remote control. If any leveling actuator  542  is adjusted manually, the control system  638  deems the machine  10  not level. The operator can input a command sequence via a remote to instruct the control system that the machine has been leveled manually and is ready to commence with normal operations. 
     Two parameters affect the sensitivity of the control system  638  to finding the floor: 1) the range of the indicator of physical force between the actuators  542  and the mine surface (i.e., the pressure gradient in the illustrated embodiment) and 2) the amount of time during which the indicator is within the specified range. The control system  638  determines whether the floor has been found by each leveling actuator  542  by measuring the displacement of the actuators  542  and detecting whether both of the parameters are satisfied. The displacement can be calculated by measuring the amount of time required for the actuator  542  to extend to a point at which the indicator of physical force reaches a predetermined value. The position at which the actuator engages the mine surface is determined by measuring either a parameter related to the elapsed time or the extension length of the actuator. After a leveling actuator  542  finds the floor, each actuator  542  is retracted a few millimeters so that the force applied by the individual actuator  542  does not affect readings for the other leveling actuators  542 . 
     Once each of the four leveling actuators  542  have found and stored the floor position in a memory of the PLC (not shown) of the control system  638 , the actuators  542  remain stationary for a predetermined period of time (step  860 ) at the “floor found” position. The leveling actuators  542  then retract for a predetermined period of time and then stopped (step  870 ). Next, the leveling actuators  542  are extended until each actuator  542  reaches the “floor found” position plus a desired offset distance (step  880 ). If the leveling actuator  542  extends beyond a maximum extension range, the automatic extend sequence  800  is aborted. Once the desired position is reached, the proportional valve  662  is set to a neutral position to stop the leveling actuators  542  (step  890 ). 
     The automatic retract sequence  900  is used to un-level the mining machine  10  (i.e., to put the machine  10  back on tracks  24 ). As shown in  FIG. 19 , the automatic retract sequence includes the first step  910  of actuating the proportional valve  662  to a retract set point. This enables the leveling actuators  542  to retract upwards simultaneously (step  920 ). Once all of the leveling actuators  542  are in the minimum position, the sequence ends (step  930 ). 
     The leveling actuators  542  may be lowered individually to prevent the center of gravity of the mining machine  10  from shifting. Referring to  FIG. 20 , the individual leveling sequence  1000  includes the first step  1010  of disabling all leveling actuators  542  and setting scaled joystick values to neutral. The next step  1020  is to select a direction for the leveling actuators  542  to move. Then, the scaled joystick value is calculated for the selected direction (step  1030 ). The proportional valve  662  is then set to a scaled joystick value and the individual leveling actuator  542  is actuated (step  1040 ). Once the leveling actuator  542  is leveled, the actuator  542  is stopped (step  1050 ). This process is repeated until all of the leveling actuators  542  are leveled. 
     After the mining machine  10  is leveled, support actuators  546  are activated to engage the roof and ensure that the machine  10  is adequately anchored during the cutting operation. In one embodiment, the control system  638  is interlocked to allow support actuators  546  to engage the roof after a leveling sequence is completed and not vice versa, in order to prevent damage to the tracks  24 . 
     As shown in  FIG. 21 , the controller includes an automatic stabilization sequence  1100  for stabilizing the support actuators  546  against the hanging wall or roof. From an idle state (step  1105 ), the stabilization sequence is initiated (step  1110 ) and the controller disables the first permissive valve  682  and the second permissive valve  686  for each support actuator  546  (step  1120   a ). In the illustrated embodiment, the controller reduces fluid flow to zero (step  1120   b ) and reduces pressure to zero (step  1120   c ). The controller then ramps, or gradually increases, the pressure to a minimum pressure level and ramps the flow to a minimum flow level (step  1130 ). Next, the controller determines whether the “raise” sequence is selected (step  1140 ). As described above, the operator can actuate the support actuators  546  by, for instance, pressing a combination of buttons on the remote control together with moving the joystick in a desired direction (i.e., up or down). All support actuators  546  are activated simultaneously during the stabilization sequence  1100 . 
     If the raise sequence is selected, the controller activates the first permissive valves  682  (step  1150 ) to maintain a set extension speed. In the illustrated embodiment, the controller also unlocks the pilot-operated check valves  690 , thereby allowing the flow to ramp to a predetermined value or set point (step  1160 ) and the pressure to ramp to a predetermined value or set point (step  1170 ). 
     In the illustrated embodiment, the pressures in the support actuators  546  are monitored as the support actuators  546  extend. The control system  638  determines that the headboard  550  has engaged the roof when at least one indicator of the force between the actuator  546  and the roof reaches a predetermined value. This indicator may include, for example, the pressure in the actuator  546 . The control system  638  compares the measured extension time and extension length of the actuator  546  against a maximum permitted extension time and extension length, respectively. That is, if the stabilizer pressure does not increase to the preset pressure value within a pre-determined actuator extension range and within a preset time, the operation times out (step  1175 ). This causes all of the stabilizers  534  to stop and the auto stabilization sequence  1100  is aborted. 
     In the illustrated embodiment, when all of the headboards  550  touch the roof, the controller checks whether the positions of the support actuators  546  are within an operational range. If so, the indicator increases until a predetermined value is reached (step  1180 ). In the illustrated embodiment, extra pressure is applied until a pre-determined pressure set point is reached. The pressure set point is maintained mechanically, independent of the control system  638 . During an “auto-cut” or “find face” control sequence of operation of the machine, the actuator indicators (i.e., the pressures and positions in the illustrated embodiment) are monitored. If the indicator of force between the actuator  546  and the roof falls below the predetermined value, then the mining machine  510  is deemed unsupported and all command sequences are aborted. When all support actuators  546  are engaging the roof, the stabilizers  534  are automatically re-energized until the indicator of force for each actuator reaches the predetermined value. When the predetermined value is achieved in all support actuators  546 , the operator receives an indication from, for instance, an indicator light or from the remote control. At this point, other machine operations (such as, for example, a “find face” or automatic cutting sequence) can be performed. Since the full force of the actuators  546  is not applied until all support actuators  546  are in place, the force is evenly distributed on the roof. 
     If the “raise” sequence is not selected, the controller determines if the “lower” sequence is selected (step  1240 ). The “lower” sequence may be selected by actuating the remote control (including, for instance, moving the joystick downward in combination with pressing other remote control buttons) to retract the support actuators  546 . If the “lower” sequence is selected, the controller activates the second permissive valves  686  (step  1250 ) to maintain a set retraction speed. The controller also unlocks the check valves  690 . In the illustrated embodiment, this permits the controller to ramp the flow to a predetermined value or set point (step  1260 ), and then ramp the pressure to a predetermined value or set point (step  1270 ). The support actuators  546  then retract until they have retracted a predetermined distance (step  1280 ). 
     Thus, the invention provides, among other things, a stabilization system for a mining machine. Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described. Various independent features and independent advantages of the invention are set forth in the following claims.