Patent Publication Number: US-6334396-B2

Title: Switch stoneblower

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to railroad track maintenance equipment and more particularly to a vehicle for performing maintenance on the bed of a railroad track. 
     It is important for railroad track to remain substantially level and uniform along its length. Although slight and gradual variations in the profile of the track are typically acceptable, rapid or severe longitudinal or lateral variations can have a significant impact on the performance of the track. As a result, significant efforts are made to maintain the railroad track with a level profile. To this end, railroad track is typically laid on a bed of ballast stones, which provide a firm foundation for the ties or sleepers. Once the track is leveled, the ballast stone bed helps to preserve the level of the track for a relatively long period of time. Nonetheless, over extended use the stones shift, crumble or otherwise degrade causing undesired variations in the track, such as bows, twists and undulations. For example, stone under one end of a particular tie may shift or crumble under repeated train passes causing that end of the tie to settle. As the tie settles, it creates a low spot in the rail, making travel over the rail rough and, depending on the severity, possibly increasing the likelihood of a derailment. 
     To maintain the level of a railroad track, it is necessary to perform periodic maintenance on the railroad track bed. One particularly effective method for maintaining a railroad track bed is to supply new ballast stones to the bed beneath settled ties. Typically, the new ballast stones are blown under the tie using compressed air. As a result, this method is commonly referred to as “stoneblowing.” Stoneblowers have been in use for years and provide significant advantages over other maintenance techniques. For example, experience has revealed that track that is maintained by stoneblowing may retain a level profile significantly longer than track maintained using conventional “tamping” methods. 
     Stoneblowing is typically performed by a track maintenance vehicle, called a stoneblower. A stoneblower typically includes a jack for lifting the railroad track and associated ties and at least one workhead for delivering new stone under the lifted ties. A stoneblower workhead typically includes a pair of blowing tubes that can be thrust into the ballast adjacent to the tie to deliver new stone. The blowing tubes are positioned on the workhead to straddle the rail and supply stone on opposites sides of the rail. In use, the blowing tubes are typically aligned with the edge of the tie and include openings toward their lower ends to allow ballast to blown directly beneath the tie. A conventional workhead is mounted toward the bottom of the vehicle on a pair of movable carriages. The carriages permit a limited range of lateral and longitudinal movement of the workhead. Conventional stoneblowers are not well-suited for use in maintaining switches and other complex track configurations. The double carriage arrangement of a conventional workhead often fails to provide enough adjustment to accommodate the complex tie and rail arrangements found in switches and the like. Also, the dual blowing tube workhead is not well-suited for treating many locations in a switch as one blowing tube may impede insertion of the other into narrow locations. 
     SUMMARY OF THE INVENTION 
     The aforementioned problems are overcome by the present invention wherein a stoneblower is provided with a vertically extended workhead that pivots from a point located near the top of the stoneblower. The position of the workhead is controlled by a pair of hydraulic cylinders operatively connected to a central portion of the workhead. In a preferred embodiment, the workhead includes a single blowing tube extending downwardly from the bottom of the workhead. 
     In a more preferred embodiment, the stoneblower includes a computerized control system for controlling the position of the workheads. The control system includes an automated height control system that automatically positions the blowing tube at the desired height regardless of the left/right (or lateral) position of the workhead. The uniform height control system automatically adjusts the position of the vertical cylinder to compensate for changes in the height of the blowing tube that would otherwise result from arcuate movement of the workhead. 
     In an even more preferred embodiment, the workhead includes two pair of workheads, a first pair located over the left rail and a second pair located over the right rail. Each pair of workheads includes a forward workhead having a rearwardly opening blowing tube and a rear workhead having a forwardly opening blowing tube. The forward and rear workheads are adapted to align with the forward and rearward faces of a tie, respectively. 
     The present invention provides an effective stoneblower that is particularly well suited for maintaining switches and other complex track configurations. The workheads are easily adjustable to treat even narrow locations in the rail. Because the workhead pivots near the top of the vehicle, increased fore/aft and left/right movement is possible with only a relatively small amount of vertical movement. The pivotal mounting permits a broad range of movement of the workhead without requiring a correspondingly broad range of movement in the actuating assembly. In fact, the workhead can even treat locations outside of the lateral profile of the vehicle. Further, the automated height control system permits left and right adjustment of the workhead without requiring manual adjustment of the height of the workhead. 
     These and other objects, advantages, and features of the invention will be readily understood and appreciated by reference to the detailed description of the preferred embodiment and the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a side elevational view of a first portion of a stoneblower in accordance with a preferred embodiment of the present invention; 
     FIG. 1 b  is a side elevational view of a second portion of the stoneblower; 
     FIG. 2 is an enlarged side elevational view of a central portion of the stoneblower; 
     FIG. 3 is a top plan view of a central portion of the stoneblower; 
     FIG. 4 is a partial sectional view of the stoneblower with portions removed taken along line IV—IV of FIG. 2; 
     FIG. 5 is front elevational view of the workhead; 
     FIG. 6 is a side elevational view of the workhead; 
     FIG. 7 is a top plan view of the workhead; 
     FIG. 8 is a front elevational view of the vertical cylinder; 
     FIG. 9 is a side elevational view of the vertical cylinder; 
     FIG. 10 is a section view of the vertical cylinder taken along line X—X of FIG. 8; 
     FIG. 11 is a top plan view of the vertical cylinder; 
     FIG. 12 is a top plan view of the longitudinal cylinder assembly; 
     FIG. 13 is a front elevational view of the longitudinal cylinder assembly; 
     FIG. 14 is a sectional view of the longitudinal cylinder assembly taken along line XIV—XIV of FIG. 12; 
     FIG. 15 is a side elevational view of a portion of the stoneblower showing the workhead actuating assembly; 
     FIG. 16 is top plan view of a portion of the stoneblower showing the workhead actuating assembly; 
     FIG. 17 is a top plan view of a central portion of the stoneblower with portions removed showing the workheads and the associated actuating assemblies; and 
     FIG. 18 is a perspective view of a workhead an actuating assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A stoneblower incorporating the present invention is shown in FIG.  1  and generally designated  10 . The stoneblower generally includes a superstructure  12 , trucks  14   a-b  for rollingly supporting the superstructure on a railroad track, a jackbeam  16  for lifting the track and attached ties, a supply of ballast stones  18  carried in a stone hopper  20 , and a plurality of workheads  22  for delivering the ballast stones  18  under the lifted tie. Generally, stoneblowers and their operation are known to those skilled in the art. Therefore, only a brief description of the stoneblower&#39;s operation is provided. The stoneblower  10  of the present invention is specially adapted to perform maintenance on switches and other complex rail arrangements. In operation, the stoneblower  10  travels along the track to a location that requires maintenance. These locations are by typically determined using any of a variety of well-known rail profiling techniques. The measured track profile is used to calculate which ties require additional ballast and how much ballast should be supplied. A suitable track profile measuring system carried by the stoneblower is disclosed in U.S. Pat. No. 5,605,099 entitled MAINTENANCE VEHICLE AND METHOD FOR MEASURING AND MAINTAINING THE LEVEL OF A RAILROAD TRACK and U.S. Pat. No. 5,167,639 entitled RAILROAD MAINTENANCE VEHICLE REFERENCE SYSTEM TRANSDUCER, which are incorporated herein by reference. Once the stoneblower  10  reaches a tie where additional stone is required, the jackbeam  16  is used to lift the rail and attached ties. The workheads  22  then force blowing tubes into the ballast adjacent the raised track ties. Stone is blown into the void beneath the raised ties in the appropriate quantity to level the ties. The workhead withdraws the blowing tubes, the track is lowered, and the stoneblower moves down the track to the next location. If desired, the workheads  22  can be repositioned to supply ballast stone to additional locations along the tie before the track is lowered and the stoneblower moves down the track. 
     As noted above, the stoneblower  10  includes a superstructure  12  mounted upon front and rear trucks  14   a-b.  The trucks  14   a-b  are generally conventional and will not be described in detail. Suffice it to say that the trucks  14   a-b  are adapted to travel along the railroad track and include at least one pair of drive wheels that are operatively connected to the main engine  32  to provide the stoneblower  10  with motion. The superstructure  12  is carried by the trucks  14   a-b  and includes an operator compartment  26 , a workhead section  28 , and an engine compartment  30 . Conventional controls (not shown) for driving the stoneblower  10  along the track are located at the front of the operator compartment  26 . Controls for operating the jackbeam  16  and workheads  22  are located at the rear of the operator compartment overlooking the workhead section  28  of the stoneblower  10 . These controls are described in more detail below. The workhead section  28  is located directly behind the operator compartment  26 . The workheads  22  and jackbeam  16  are mounted to the superstructure  12  in the workhead section  28 , where their operation is visible from the location of their controls in the operator compartment  26 . The engine compartment  30  is located immediately behind the workhead section  28 . The main engine  32 , air compressor  34 , battery box  36 , hydraulic mechanisms  38 , fuel tank  40  and other components are located in the engine compartment  30 . The superstructure  12  includes a framework of support beams, including left and right lower support beams  42   a-b  that extend longitudinally along opposite sides of the operator compartment  26 , left and right intermediate support beams  44   a-b  that extend longitudinally along opposite sides of the workhead section  28  and left and right upper support beams  46   a-b  that extend longitudinally along opposite sides of the workhead section  28  and the majority of the engine compartment  30 . The lower support beams  42   a-b,  intermediate support beams  44   a-b  and upper support beams  46   a-b  are interconnected by a plurality of vertical support beams  48 . A plurality of lateral support beams  50  interconnect the left and right support beams  42   a-b,    44   a-b  and  46   a-b.  A pair of workhead support beams  62   a-b  extend longitudinally between the lateral support beams  50 . As described in more detail below, the workheads  22   a-d  are pivotally mounted to the workhead support beams  62   a-b.  The described superstructure  12  is merely exemplary, and its design and configuration may vary from application to application. 
     The stoneblower  10  preferably includes four workheads  22   a-d,  arranged in left and right pairs. Each pair including a forward workhead  22   a  and  22   c  with a single blowing tube opening rearwardly and a rear workhead  22   b  and  22   d  with a single blowing tube opening forwardly. The workheads  22   a-d  are positioned on opposite sides of a tie T to blow stone under the tie from opposite directions. A single workhead  22  is illustrated in FIG.  18 . The workhead  22  includes a vertical cylinder  54  mounted within a rectangular sleeve  56  (See FIGS.  5 - 7 ). The sleeve  56  is mounted to the superstructure  12  by a universal joint  58  that permits the workhead  22  to pivot both laterally and longitudinally. The universal joint  58  includes a mounting rod  58  fixedly secured to the upper end of the sleeve  56 . A clevis  60  is pivotally mounted on the rod  58  using conventional bearings or bushings (not shown). The clevis  60  is in turn pivotally mounted to the corresponding workhead support beam  62   a  or  62   b  extending between lateral support beams  64  and  65 , again using conventional bearings or bushings (not shown). The vertical cylinder  54  is pivotally mounted within the rectangular sleeve  56  (See FIGS.  8 - 11 ). The upper end of the vertical cylinder  54  is pivotally mounted to the approximate center of the sleeve  56  on axle  66 . The axle  66  is rotatably received within fittings  68   a-b  that house appropriate bearings or bushings (not shown). This provides the vertical cylinder  54  with a limited range of forward and rearward pivotal motion, which as described below is used in sensing the location of a tie. A pair of resilient couplings  70  interconnect the vertical cylinder  54  and the sleeve  56  just inside the bottom of sleeve  56  to bias the vertical cylinder  54  in a home position within the sleeve  56 . The couplings  70  are preferably secured to the vertical cylinder  54  by collar  124 . As perhaps best shown in FIG. 6, the home position H is preferably offset 1° from the vertical axis V of the rectangular sleeve  56  toward the direction of the blowing tube opening. As described in more detail below, this 1° “pre-tilt” permits the vertical cylinder and rectangular sleeve  56  to come into vertical alignment once the vertical cylinder tilts 1° upon engagement with a tie face. The couplings  70  are preferably manufactured from rubber or other similarly flexible and resilient materials. A transducer  72  or other similar sensing device is mounted to the vertical cylinder  54  and sleeve  56  to sense pivotal movement of the vertical cylinder  54  with respect to the sleeve  56 . The lower end of the vertical cylinder  54  protrudes from the sleeve  56  to receive a blowing tube holder  74 . 
     The vertical cylinder  54  is extended and retracted using conventional hydraulics. Referring now to FIGS. 8-11, the vertical cylinder  54  includes rod  100  slidably fitted within cylinder wall  102 . The cylinder wall  102  includes a closed end  103  and an open end  105 . A ring  108  and ring seal  109  are fitted within the open end  105  to close the cylinder wall  102 . A pair of conventional fittings  104  and  106  are mounted in opposite ends of the cylinder wall  102  to supply and exhaust hydraulic fluid in a conventional manner. A piston  110  is secured to the inner end of the rod  100  to divide the interior of the cylinder wall  102  into two distinct voids. A stop tube  111  is fitted over the rod  100  adjacent the piston  110 . The stop tube  111  engages the inner surface of the ring seal  108  to limit the stroke of the rod  100 . A conventional transducer  112  is mounted through the closed end  104  of the cylinder wall  102 . The transducer  112  includes a shaft  114  that extends into a concentric bore  116  defined in the center of rod  100  and a ring  118  that is mounted to the rod  100  around shaft  114 . The transducer  112  provides accurate measurement of the position of the rod  100  within the cylinder wall  102 , and consequently of the vertical position of the blowing tube  82 . A collar  120  is attached to the lower end of the rod  100  outside of the cylinder wall  102 . A guide rod  122  is rigidly affixed to the collar  120 . A second collar  124  is mounted to the cylinder wall  102 . The second collar  124  defines a guideway  126  that slidably receives the guide rod  122 . Cooperatively, these components prevent the rod  100  from rotating within the cylinder wall  102 . 
     The workhead  22  includes a latch assembly  94  for securing the blowing tube  82  in the raised position during travel (See FIG.  4 ). The latch assembly  94  includes a hook  130  that is pivotally secured to the rectangular sleeve  56  and a conventional hydraulic cylinder  132  for controlling movement of the hook  130 . The latch assembly  94  further includes a catch  134  defined in collar  120 . In operation, cylinder  132  can be extended to cause hook  130  to engage catch  134 , thereby locking the blowing tube  82  in the raised position (See solid lines in FIG. 4) or retracted to disengage the hook  130  permitting extension of the vertical cylinder  54  (See phantom lines in FIG.  4 ). 
     In general, the blowing tube holder  74  is a vertically elongated tube having a top  138 , a bottom  140  and a neck  142  protruding at an angle to the centerline of the blowing holder  74 . The top  138  defines a mounting bore  76  that is fitted over and secured to the lower end of the sleeve  56 . The bottom  140  includes a flange  80  adapted to mount a blowing tube  82  as described below. The neck  142  defines a stone inlet  78  to receive ballast stone and an air inlet  79  to receive pressurized air. A stone passageway  84  extends from the stone inlet  78  through the flange  80  to feed ballast stone to the blowing tube  82 . An air passageway  83  extends from the air inlet  79  to the stone passageway  84 . The pressurized air flows through the stone passageway  84  creating a partial vacuum that draws in stone and expels it through the blowing tube  82 . 
     The blowing tube  82  is generally conventional and includes a vertically elongated tube having an inlet opening  86  formed in its upper end and a vertically extended exit opening  88  formed in the lower end. The lower tip  90  of the blowing tube is pointed and wedge shaped to facilitate penetration into the track ballast and to urge the blowing tube toward the tie face as the blowing tube is moved downwardly. A flange  92  extends around the blowing tube  82  to engage flange  80 . The blowing tube  82  is secured to the blowing tube holder  52  by fasteners extending through flanges  92  and  80 . 
     A flexible supply hose  148  is fitted over neck  142 . The supply hose  148  is generally conventional and is preferably manufactured from readily available wire reinforced, abrasion-resistant plastic tubing. The supply hose  148  preferably includes an internal diameter of approximately three inches, or 75 mm, and is secured to the neck  142  by a conventional clamp (not shown). As described below, the supply hose  148  receives ballast stone from the stone metering device in a conventional manner. The stone and air are supplied to the blowing tube  82  through the blowing tube holder  52 . 
     As noted above, the rectangular sleeve  56 , and consequently the entire workhead  22   a-d,  is pivotally mounted for both longitudinal and lateral movement. The position of each workhead  22   a-d  is individually controlled by a separate actuating assembly  150  that is mounted to a lateral support tube  159 . Referring now to FIGS. 15-18, the actuating assembly  150  includes a lateral adjustment assembly  152  and a longitudinal adjustment assembly  154 . The lateral adjustment assembly  152  controls lateral or transverse pivotal movement of the workhead  22 , and includes a sleeve  156  slidably fitted over the lateral support tube  159  and a lateral cylinder  158  for moving the sleeve  156  along tube  159 . Bushings  172 , bearings or other conventional friction reducing elements are fitted within the sleeve  156  to ease movement of the sleeve  156  along the tube  159 . The lateral cylinder  158  is preferably a conventional hydraulic cylinder. The first end of the cylinder  158  is fixed to the lateral support tube  158  at ear  160  and the second end is fixed to the sleeve  156  at mounting ear  162 . Both ends of the lateral cylinder  158  are attached using conventional spherical bushings to allow for slight pivotal movement of the sleeve  156  about the lateral support tube  158 . A conventional linear transducer (not shown) is fitted within the lateral cylinder  158  to sense the lateral position of the workhead  22 . 
     The longitudinal adjustment assembly  154  controls fore and aft pivotal movement of workhead  22 , and includes a longitudinal cylinder  164  secured to the sleeve  156 . Referring now to FIGS. 12-14, the longitudinal cylinder  164  extends perpendicularly from the sleeve  156  and includes a cylinder wall  166 , a piston  168  seated within the cylinder wall  166  and an extendible rod  171  interconnected with the piston  168 . The cylinder wall  166  includes a closed end  176  and an open end  178 . A ring  180  and ring seal  182  are fitted within the open end  178  to close the cylinder wall  166 . The ring  180  includes an extended stop  186  that limits the stroke of the piston  168 . The ring  180  further includes external threads  184  that engage internal threads  186  on the inner surface of the cylinder wall  166  to secure the ring  180  is place. A pair of conventional fittings  188   a-b  are mounted at the open end  178  of the cylinder wall  166  to supply and exhaust hydraulic fluid. A second pair of conventional fittings  190   a-b  are defined in the sleeve  156 . Passageways  192   a-b  extend between fittings  190   a-b  and the closed end  176  of the cylinder wall  166  to supply and exhaust hydraulic fluid. The longitudinal cylinder includes two sets of fittings  188   a-b,    190   a-b  so that at least one set of fittings (e.g.  188   a  and  190   a ) is readily accessible when the cylinder is installed on either the left or right side of the vehicle. The other set of fittings (e.g.  188   b  and  190   b ) is plugged when not in use. The piston  168  is generally conventional and is attached to the rod  170  in a conventional manner, such as by nut  194 . The rod  170  protrudes from the cylinder wall  166  and includes a mounting clevis  168  affixed to its outer end  196 . Conventional roller bearings  200  are fitted within the clevis  168 . The clevis  168  is mounted to the rectangular sleeve  56  of the workhead  22  at ear  170  in a conventional manner, such as by pin. A pair of support plates  202   a-b  are mounted between the lateral sleeve  156  and the cylinder wall  166  to provide lateral strength to the assembly. A conventional transducer (not shown) is mounted external to the longitudinal cylinder  164  to sense the longitudinal position of the workhead  22 . 
     The workheads  22   a-d  are controlled by a computerized control system (not shown). The controls include separate joystick controls (not shown) for the left pair of workheads  22   a-b  and the right pair of workheads  22   c-d.  The joysticks control the left/right and fore/aft movement of the workhead. Eachjoystick includes a workhead selector switch (not shown) that is moveable between a first position in which the joystick controls movement of the forward workhead and a second position in which the joystick controls movement of the rear workhead. One of the two joysticks may also be used to operate the jackbeam in a conventional manner by activating a jackbeam selector switch. Alternatively, a separate joystick can be provided for operating the jackbeam. 
     The control system also includes an automated height control system (not shown) for controlling the height of the blowing tubes  82 . The automated height control system includes a uniform height control system (not shown) for positioning the blowing tubes  82  at a uniform height (e.g. in the same horizontal plane) despite the lateral disposition of the workheads  22   a-d.  Because the workheads  22   a-d  are mounted for pivotal movement, each blowing tube  82  inherently travels through an arc as it pivots left/right. Accordingly, the real height of the blowing tubes  82  for any given position of the vertical cylinder  54  would normally vary depending on the position of the workhead  22   a-d  in this arc. This would complicate operation of the stoneblower because, in order to position the blowing tube  82  at a uniform height, it would require variation in the position of the vertical cylinder  54  for any variation in the lateral position of the workhead. For example, FIG. 4 shows the blowing tube  82 ′ in phantom lines at four different pivotal positions, A, B, C, and D with the vertical cylinder  54  at a given position. As can be seen, the height of the blowing tube  82 ′ varies significantly from horizontal line L between the different positions A, B, C, and D. To address this problem, the automated height control system (not shown) automatically adjusts the vertical cylinder  54  to compensate for variations in the left/right position of the workhead  22 . In the preferred embodiment, the necessary variation in the position of the vertical cylinder  54  is computed by the formula: E =|(D/COS θ)−D FIG.l, where E is the additional amount of extension necessary to compensate for the lateral position of the workhead, D is the vertical distance from the pivot point of the workhead to the bottom of the tie T, and θ is the angle of the workhead away from its vertical center. The vertical position of the raised tie T is measured in a conventional manner by the stoneblower reference system. Because the ties have a uniform height, the location of the bottom of the tie is easily computed from the measured value. The value of θ is determined by the transducer (not shown) of the lateral cylinder  158 . In operation, the workhead  22   a-d  will be positioned so that a point 40 millimeters from the bottom of the blowing tube exit opening  88  along its vertical centerline is aligned with the bottom of the tie T. The value of 40 millimeters is used in the preferred embodiment in part because it provides adequate stone flow. This value may, however, vary from application to application. Accordingly, the uniform height control system varies the position of the vertical cylinder  54  so that a point along the vertical centerline of the blowing tube 40 mm above the bottom of the exit opening  88  aligns with the bottom surface of the tie T at all left/right pivotal locations of the workhead  22   a-d.  The automated height control system may be configured to compensate for fore/aft movement as well as left/right movement of the workhead in a similar manner, for example, by also extending and retracting the vertical cylinder in response to fore/aft movement of the workhead. 
     Referring now to FIGS. 1-3, the stoneblower  10  includes a stone supply system  200  for supplying stone to the workheads  22   a-d.  In the preferred embodiment, the stone supply system  200  includes a stone hopper  20  and four metering augers  204   a-d.  The stone hopper  20  stores a supply of ballast stones  18  and includes four outlets  206   a-d —one communicating with each of the four stone metering augers  204   a-d,  respectively. The stone hopper  20  feeds stone into the stone metering augers  204   a-d  through outlets  206   a-d  by gravity. The stone metering augers  204   a-d  are generally conventional and function to supply ballast stone to the workheads  22   a-d,  respectively. Each stone metering auger  206   a-d  includes a casing  208   a-d  having an inlet (not shown) positioned directly below the corresponding stone hopper outlet  206   a-d  and an outlet (not shown) at the opposite end of the casing  208   a-d  through which metered stone flows into the supply hose  148 . A screw  210  is rotatably supported within the casing  208   a-d  of each stone metering auger  206   a-d  to both meter the stone and move it from the inlet to the outlet (See FIG.  3 ). From the outlet, the stone falls into the supply hose  148  where it is drawn by gravity and air entrainment into the blowing tubes  82 . The described stone supply system  200  is merely exemplary and may be replaced by virtually any system capable of supplying metered stone to the workhead. For example, the stone metering augers  204   a-d  can be replaced by other conventional stone metering devices and the stone hopper  20  can be replaced by other conventional ballast stone storage devices. 
     Operation 
     For simplicity and clarity, the operation of the present invention is described in connection with the operation of a single workhead during maintenance of a switch. It should be readily apparent that the operation may be extended to virtually any number of workheads. 
     The stoneblower is particularly well suited for use in maintaining switches and other complex track configurations. As noted above, the profile of the track is measured using any of a variety of well-known rail profiling techniques. From the profile, the ties requiring maintenance are identified and the volume of ballast stone to be blown beneath each of those ties is computed. The stoneblower is then manually moved over the rails to the appropriate location to perform maintenance on the first tie requiring maintenance. After the stoneblower has traveled to the location requiring maintenance and prior to positioning of the workhead, the latch assembly  94  must be moved into the unlocked position (See phantom lines in FIG.  4 ). The latch assembly  94  is operated by conventional controls, such as a toggle switch (not shown) located near the joystick controls. The latch assembly  94  preferably remains unlocked while the stoneblower performs maintenance on and indexes through the section of track requiring maintenance. The latch assembly  94  is locked again after maintenance is stopped and the stoneblower is ready to travel. 
     Once the stoneblower is properly positioned along the track, the rails and attached ties are lifted using the jackbeam  16 . The jackbeam  16  is preferably operated using a generally conventional joystick (not shown). The jackbeam  16  may share a joystick with one of the workhead pairs, as noted above. The jackbeam  16  is manually positioned adjacent to the rails using the joystick in a conventional manner. Once positioned, the user depresses the jackbeam cycle button (not shown) and the jackbeam control system automatically clamps and lifts the rails in a conventional manner to the height desired to perform maintenance. 
     Once the rails and ties are lifted, the workheads  22   a-d  are moved into position to blow the appropriate volume of ballast stone beneath the raised ties. The workheads  22   a-d  are positioned using generally conventional joysticks (not shown), and can be moved into position in any order. 
     Depending on the track profile, it may not be necessary to use all of the workheads  22   a-d  at a given location. For example, if the right side of the tie has settled while the left side has maintained the desired height, it may only be necessary to supply stone under the right side of that tie. Consequently, it may only be necessary to position and supply stone through the right workheads  22   c-d.  Movement of the joystick sends control signals to the computerized control system. The control system interprets the signals and either extends or retracts the appropriate cylinder or cylinders. For example, with the rear workheads  22   b  and  22   d,  rearward movement of the joystick results in retraction of the corresponding longitudinal cylinder and hence rearward movement of the workhead  22   b  and  22   d.  Similarly, with the left pair of workheads  22   a-b,  leftward movement of the joystick results in extension of the corresponding lateral cylinder and hence leftward movement of the workheads  22   a-b.  With the right pair of workheads  22   c-d,  leftward movement of the joystick results in retraction of the corresponding lateral cylinder and hence leftward movement of the workheads  22   a-b.    
     In operation, the joystick is manipulated to manually move the workhead  22   a-d  into a position adjacent the tie T where maintenance is to be performed. The blowing tube  82  is positioned at the desired lateral position a small distance from the face of the tie T. Once the workhead  22   a-d  is properly positioned, the user depresses the workhead cycle button (not shown) to activate the control system. Upon depression of the workhead cycle button, the control system automatically moves the blowing tube  82  into engagement with the tie face and then thrusts it down into the ballast to the desired height. More specifically, the control system first swings the workhead  22   a-d  toward the tie by extending or retracting the longitudinal cylinder  164  until it determines that the blowing tube  82  has engaged the tie face. As noted above, the vertical cylinder is provided with a 1° pre-tilt which permits the vertical cylinder to pivot 1° with respect to the rectangular sleeve  56  upon contact with a tie face during positioning. This 1° pivot is used as a key to indicate that a tie has been located. In operation, the workhead  22   a-d  travels freely until it engages the face of the tie T. Continued movement of the workhead  22   a-d  toward the tie causes the vertical cylinder  54  to pivot with respect to the rectangular sleeve  56 . The longitudinal transducer (not shown) senses relative movement between the vertical cylinder  54  and the sleeve  56  and provides corresponding signals to the computer control system. Once these signals indicate that the vertical cylinder  54  has pivoted 1° with respect to the sleeve  56 , the computer control system stops movement of the workhead  22   a-d  toward the tie and then lowers the blowing tube into the ballast to the desired height. 
     As noted above, the vertical position, or height, of the workhead  22   a-d  is controlled by the automated control system. The control system extends or retracts the vertical cylinder  54  to position the blowing tube at the desired height. Experience has revealed that it is desirable to position the blowing tubes  82  so that the area of the exit opening  88  positioned below the tie is consistent. This reduces the likelihood of clogging and facilitates proper stone metering. As noted above, the vertical cylinder  54  is preferably positioned so that a point along the vertical centerline of the blowing tube 40 mm above the bottom of the exit opening  88  is aligned with the bottom surface of the tie T. This distance may, however, vary from application to application. The desired depth of the blowing tubes will be input into the control system, typically prior to maintenance. The uniform height control system (not shown) facilitates uniform vertical positioning of the blowing tubes  82  by automatically adjusting the height of the blowing tube  82  to compensate for left/right movement of the workhead. After depression of the workhead cycle button, the control system determines the lateral position of the workhead by way of the linear transducer (not shown) of the lateral cylinder  158 . The uniform height control system then computes any variation in the position of the vertical cylinder  54  necessary to compensate for the lateral position of the workhead  22   a-d.  As noted above, the vertical position of the raised tie T is measured by the stoneblower reference system (not shown) and serves as a reference point for use in computing any necessary variation in the position of the vertical cylinder  54 . Once this value is computed, the uniform height control system automatically extends the vertical cylinder  54  the computed amount, thereby driving the blowing tube  82  down into the ballast to the desired vertical position. In the preferred embodiment, the uniform height control system does not compensate for fore and aft movement of the workhead, but that capability may be added as desired. After the workhead(s)  22   a-d  is properly positioned, the stone supply system  200  is operated to supply the desired volume of stone to the workhead(s)  22   a-d.  The volume of stone supplied to each workhead  22   a-d  is preferably dictated by automated control. The control system (not shown) uses the information collected from the measured track profile to determine the appropriate amount of stone for each workhead  22   a-d.  The control system (not shown) supplies the appropriate volume of stone to a given workhead  22   a-d  by operating the stone metering device for that workhead  22   a-d  (e.g. the stone metering auger  204   a-d ) at a specified supply rate for a specified period of time. 
     Once the desired volume of stone has been blown beneath the tie, the control system automatically stops the stone supply system  200  and raises the workheads  22   a-d  into a home position by retracting the vertical cylinder  54 . The home position is high enough for the blowing tubes  82  to clear the ties as the stoneblower moves along the track. The jackbeam  16  then lowers the track, and the stoneblower  10  is ready to move, or index, along the track to the next location requiring maintenance. This cycle is typically repeated for the entire length of track requiring maintenance. Once maintenance is complete or it is otherwise necessary for the stoneblower to travel from the section of track being maintained, the workheads  22   a-d  are fully raised and the latch assembly  94  for each is locked. 
     The stoneblower  10  is also well suited for maintaining plain line track. When operating on plain line track, the stoneblower&#39;s movement along the track is largely automated and operates under computer control. The superstructure  12  moves along the track by indexing movement with respect to the ties. At each indexed location, the workheads  22   a-d  are moved into the appropriate location to perform maintenance manually. 
     The computer control directs movement of the stoneblower based on track profile data provided by the track measuring system. As noted above, the track profile data is collected prior to and/or during the maintenance pass of the stoneblower. The computer control processes the track profile data to determine which ties require maintenance. As the stoneblower moves along the track, the computer control stops the stoneblower at the appropriate ties to perform maintenance. First, the jackbeam  16  is used to lift the rail and attached ties. The jackbeam  16  operates in generally the same manner as described above. After the rail is lifted, the appropriate workhead or workheads  22   a-d  are positioned in generally the same manner as described above to supply stone to the desired location under the lifted tie. As described above, the 1° pre-tilt of the vertical cylinder is used to position workhead  22   a-d  with respect to the face of the tie. Once properly positioned, the stone supply system  200  supplies the desired volume of stone. After the appropriate volume of stone has been supplied, the workheads  22   a-d  are raised into the home position and the track is lowered. The stoneblower  10  is then ready to move along the track to the next location requiring maintenance. The above description is that of a preferred embodiment of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular.