Railroad car wheel handler and method

Information

  • Patent Grant
  • 6675719
  • Patent Number
    6,675,719
  • Date Filed
    Tuesday, July 2, 2002
    22 years ago
  • Date Issued
    Tuesday, January 13, 2004
    20 years ago
Abstract
A railroad car wheel changer assembly (10), adapted to be mounted on a gantry crane (12), is provided. The railroad car wheel changer assembly (10) includes a base assembly (60), a beam member (62) and a grappler assembly (64). The base assembly (60) is adapted to be attached to the gantry crane(12). The beam member (62) is attached to the base assembly (60). The grappler assembly (64) is adapted to engage a railroad car wheel assembly (100) and is attached to a first end of the beam member (62). The beam member (62) is articulatable to move the wheel assembly (100).
Description




TECHNICAL FIELD




The present invention relates to an apparatus for handling a wheel assembly of a railroad car and, more particularly, to a gantry crane that can both lift the railroad car and handle the wheel assembly such as when changing the wheel assembly.




BACKGROUND OF THE INVENTION




The wheel assemblies of railroad cars generally include an axle and two flanged wheels fitted thereon. Typically, two wheel assemblies are attached to an articulating wheel truck. The condition of the wheel assemblies of railroad cars deteriorates over time. Such deterioration may result from normal use or from an accident or other incident causing sudden damage. Therefore, wheel assemblies must periodically be replaced.




Such replacement requires both an ability to lift the railroad car itself and an ability to replace or exchange the wheel assemblies. Typically, each of these functions is performed by a different or separate piece of machinery.

FIG. 1

schematically shows a prior method of changing a wheel assembly. As shown, a jack may be placed under the coupling between two cars, or a boom crane or other type of mobile crane is positioned along side of the railroad car for raising the car. Prior to lifting or hoisting, the wheel assembly to be replaced is disconnected from its wheel truck so it remains on the track. Either the entire car or just the end of the car having the wheel assembly to be replaced is lifted.




Once lifting of the railcar is accomplished, a forklift, for example, having an attachment adapted to handle wheel assemblies removes the worn or damaged wheel assembly. The forklift is also used to replace the wheel assembly with a new or replacement assembly. The mobile crane then lowers the car and the replacement wheel assembly is properly attached.




Prior art methods for handling railroad car wheel assemblies have proven to be inefficient and cumbersome. Thus, there remains a need for an apparatus that can improve the process of handling railroad car wheel assemblies.




The present invention is provided to solve these and other problems.




SUMMARY OF THE INVENTION




The present invention provides an apparatus and method for handling a wheel assembly of a railroad car such as when changing the wheel assembly of the car. In particular, the present invention provides a wheel handling assembly adapted to be attached to a gantry crane or other structure.




According to a first aspect of the invention a railroad car wheel changer assembly adapted to be mounted on a gantry crane is provided. The wheel changer assembly comprises a base assembly adapted to be attached to a gantry crane, a beam member attached to the base assembly and a grappler assembly, adapted to engage a railroad car wheel assembly. The grappler assembly is attached to a first end of the beam member and the beam member is articulatable to move the wheel assembly.




According to another aspect of the invention, the beam member comprises a telescoping boom assembly.




According to another aspect of the invention the telescoping boom assembly comprises a first boom section pivotally attached to the base assembly and a second boom section adapted to telescope within the first boom assembly wherein the grappler assembly is attached to the second boom section.




According to another aspect of the invention, the base assembly comprises an upper base portion attached to the gantry crane, a lower base portion and a slewing mechanism. The beam member is attached to the lower base portion and the slewing mechanism rotationally connects the lower base portion to the upper base portion for rotational movement of the lower base portion with respect to the upper base portion in a generally horizontal plane.




According to another aspect of the invention the changer assembly further comprises a cylinder pivotally attached to both the base assembly and the beam member for rotating the beam member generally vertically about the base assembly.




According to another aspect of the invention the cylinder is attached to a second end of the beam member.




According to another aspect of the invention, a method of changing a railroad car wheel assembly attached to a wheel truck of a railroad car is provided. The method comprises the steps of providing a gantry crane having a railroad car wheel changer assembly attached thereto; positioning the gantry crane to straddle the railroad car; positioning the changer assembly to be adjacent the wheel assembly to be changed; disconnecting the wheel assembly from the wheel truck; raising at least an end of the railroad car with the gantry crane an adequate distance to permit the wheel assembly to be moved underneath the truck; engaging the wheel assembly with the changer assembly; lifting the wheel assembly with the changer assembly; swinging the wheel assembly clear of the wheel truck; and disengaging the wheel assembly.











Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings.




BRIEF DESCRIPTION OF THE DRAWINGS




To understand the present invention, it will now be described by way of example, with reference to the accompanying drawings in which:





FIG. 1

is a schematic view showing one prior art method of changing a wheel assembly of a railroad car;





FIG. 2

is a side view of a gantry crane having a railroad car wheel handling assembly of the present invention;





FIG. 3

is a top view of a gantry crane with the railroad car wheel handling assembly;





FIG. 4

is a rear view of a gantry crane with the railroad car wheel handling assembly;





FIG. 5

is perspective view of a spreader attachment for the gantry crane; and





FIG. 6

is a partial perspective view of the wheel handling assembly connected to a lower side beam of the gantry crane, the assembly engaging a railroad wheel assembly.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT




While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated.





FIG. 2

shows a railroad car wheel handling assembly


10


connected to a gantry crane


12


. However, it is understood that the assembly


10


can be connected to other types of cranes or structures.




The gantry crane


12


generally includes a gantry structure


14


having a right side support frame


16


and a left side support frame


18


(FIG.


3


). As the right side support frame


16


and the left side support frame


18


are substantially identical in all significant respects, only the left side support frame


18


is described in detail herein.




Referring to

FIG. 2

, the left side support frame


18


includes a left front vertical leg


20


, a left rear vertical leg


22


, a left upper side beam


24


and a left lower side beam


26


. An upper cross beam


28


extends between and is connected to the right side support frame


16


and the left side support frame


18


. A left front wheel


30


is located near a lower end of the left front vertical leg


20


and a left rear wheel


32


is located near a lower end of the left rear vertical leg


22


. The right side support frame has a similar pair of wheels, not shown. Together the four wheels allow for a mobile gantry structure


14


. An operator cab


34


is shown attached to the left side support frame


16


. It is understood that the operator cab


34


can take other forms and be positioned at different locations. The operator cab


34


could also be mounted for movement between various locations.




A left front load block


36


and a left rear load block


38


are attached to the left side support frame


16


. A right front load block


40


and a right rear load block


42


are similarly attached to the right side support frame


18


. Attached to and suspended from the four load blocks is a spreader attachment


44


. The load blocks


36


-


42


operate collectively to raise and lower the entire spreader attachment


44


. The load blocks


36


-


42


and spreader attachment


44


function to lift a railroad car when changing a wheel assembly as explained in greater detail below.




As shown in

FIGS. 2-5

, the spreader attachment


44


has a plurality of interconnected beams


43


including a central beam


47


. The beams


43


are connected to the load blocks


36


-


42


. As shown in

FIG. 5

, a trolley


45


is mounted on the central beam


47


. Attached to the trolley


45


is an eye hook


46


. As shown in

FIG. 4

, depending from and attached to the eye hook


46


is a first sling


48


with a first sling hook


50


and a second sling


52


with a second sling hook


54


. As further shown in

FIG. 4

, a hydraulic cylinder


49


is connected between the spreader attachment


44


and the trolley


45


. The cylinder


49


and trolley


45


cooperate to permit lateral positioning of the eye hook


46


within the gantry structure


14


when aligning the eye hook


46


and sling hooks


50


,


54


for lifting a railroad car.




As further shown in

FIGS. 2-6

, the wheel handling assembly


10


generally includes a base assembly


60


, a beam member in the form of a telescoping boom assembly


62


and a grappler mechanism


64


.




The base assembly


60


includes an upper base portion


66


, a lower base portion


68


and a slewing mechanism


70


. As shown (FIG.


6


), the upper base portion


66


is slidingly mounted to a lower right side beam


27


via a connecting mechanism


80


. The connecting mechanism


80


includes a pair of rail tracks


82


, a double-ended hydraulic cylinder


84


and a proximity switch


86


. The rail tracks


82


are welded or other wise connected to the underside of the lower side beam


27


. The upper base portion


66


has a plurality of fingers


67


that fit around and ride along the rail tracks


82


as shown. Appropriate lubrication or slide bearings are included between the fingers


67


and the rail tracks


82


as needed. The proximity switch


86


is located near the center of the side beam


27


for detecting the longitudinal position of the base assembly


60


along the side beam


27


. Each end of the double ended cylinder


84


is attached at an appropriate location on the side beam


27


. The cylinder


84


is controlled via known hydraulic means. It is understood that other motive means may be employed to move the assembly


10


along the lower side beam


27


.




The lower base portion


68


of the base assembly


60


is rotationally mounted to the upper base portion


66


by the slewing mechanism


70


. Thus the slewing mechanism


70


operably connects the upper base portion


66


and the lower base portion


68


. The slewing mechanism


70


controls and permits the slewing, or rotational movement of the lower base portion


68


, and therefore the boom assembly


62


, in a generally horizontal plane. One end of a first or luffing hydraulic cylinder


74


is attached to the lower base portion


68


. Luffing refers to generally vertical rotation of the boom assembly


62


about the base assembly


60


. Luffing results in the vertical raising and lowering of an end of the boom assembly


60


, to be explained.




The beam member


62


or telescoping boom assembly


62


includes a first boom section


76


and a second boom section


78


. The first boom section


76


is pivotally attached to both the lower base portion


68


and the luffing hydraulic cylinder


74


. The first boom section


76


is tubular. The second boom section


78


is also tubular and is adapted to telescope within the first boom section


76


. Not shown, but easily understood by those skilled in the art, is a hydraulic boom mechanism that effects the extension and retraction of the second boom section


78


with respect to the first boom section


76


. It is further understood that additional boom sections can be employed, such as a third boom section telescoped within the second boom section


78


.




It can be seen then, that the slewing mechanism


70


, the luffing cylinder


74


, and the hydraulic boom mechanism each provide separate means by which the beam member or telescoping boom assembly


62


may articulate with respect to the base assembly


60


and the upper base portion


66


. Alternative means may be utilized to provide the desired movements of the boom assembly


62


. For example, a universal ball joint and known hydraulic actuators may be provided between the upper base portion


66


and the lower base portion


68


to provide a means of articulation of the boom assembly


62


.




The cross section of the first and second boom sections


76


,


78


can be of any shape suitable for withstanding the stresses involved in handling railroad car wheel assemblies


100


. Appropriate cross sections are known and can be determined by those skilled in the art. Additionally, the first and second boom sections


76


,


78


are made of material suitable for withstanding the anticipated loads and stresses involved in handling railroad car wheel assemblies


100


. In the particular embodiment described herein, the cross section of the first and second boom sections


76


,


78


is generally rectangular and their material of construction is a suitable grade of steel.




As shown in

FIGS. 2 & 4

, the grappler mechanism


64


includes grippers


82


and a clamp cylinder


88


. The grippers


82


include two lower stabilizing or positioning claws


92


and an upper locking claw


90


. The clamp cylinder


88


is pivotally attached at one end to the grappler mechanism


64


and is pivotally attached at another end to the locking claw


90


. The clamp cylinder


88


moves the locking claw


90


between locked and unlocked positions. The locked position is best shown in FIG.


4


. When in the locked position the lock claw


90


cooperates with the stabilizing claws


92


to grasp, hold or engage the rail wheel assembly


100


as shown. When the upper locking claw


90


is raised from the locked to un-locked position, the locking claw


90


cooperates with the stabilizing claws


92


to release the rail wheel assembly


100


.




In operation and as shown in

FIG. 6

, the wheel handling assembly


10


is capable of five functions or directions of movement. First, the entire telescoping boom assembly


62


is capable of horizontal rotation about upper base portion


66


via the slewing mechanism


70


(See Arrow A). Second, the telescoping boom portion


66


is capable of vertical rotation or luffing with respect to the lower base portion


68


via the luffing hydraulic cylinder


74


(See Arrow B). Third, the grappler mechanism


64


is capable of linear movement towards and away from the base assembly


60


via the telescoping boom assembly


62


(See Arrow C). Fourth, the grippers


82


are capable of movement to effect locking onto or grasping of a railroad car wheel assembly (See Arrow D). Finally, the entire handling assembly


10


is capable of traversing the length of the lower right side beam


26


via the connecting mechanism


80


. (See Arrow E.)




To change a railroad car wheel assembly


100


, the gantry crane


12


with wheel handling assembly


10


is positioned to straddle a set of railroad tracks. Located on the tracks is the railroad car


94


having a wheel assembly


100


needing replacement (FIGS.


2


-


4


). The railroad car


94


has a main body portion


96


supported by a wheel truck


98


and wheel assemblies


100


at each end. (Only one wheel truck


98


is shown in the figures for convenience.) Each wheel truck


98


, in turn rides on the track rails


99


on a pair of wheel assemblies


100


. Each wheel assembly includes a pair of flanged wheels


102


attached to an axle


104


.

FIGS. 3-5

show use of the wheel handling assembly


10


in conjunction with an intermodal railroad car


94


, or one that is capable of accommodating containers. However, it is understood that the wheel handling assembly


10


can be used to change the wheel assemblies


100


of all types of railroad cars. The gantry structure


14


is of sufficient height to permit lifting of the railroad car


94


.




The gantry crane


12


is then driven to the railroad car


94


and centered over the appropriate wheel truck


98


. When the gantry crane


12


is properly positioned, the spreader


44


is lowered, thereby lowering the first sling hook


50


and second sling hook


54


. The first and second sling hooks


50


,


54


are attached to lifting lugs on the wheel truck


98


provided as a point for applying a lifting or hoisting force. At some point before attempting to raise the railroad car


94


, the wheel assembly


100


is unattached from the wheel truck


98


. Then the railroad car


94


with wheel truck


98


is raised by the load blocks


36


-


42


raising the spreader


44


which will raise the eye hook


46


, first and second slings


48


,


52


and first and second sling hooks


50


,


54


, thereby raising the railroad car


94


. As the wheel assembly


100


was previously unattached from the railroad car, it remains on the rails. The wheel truck


98


is raised an adequate distance to allow the wheel assembly


100


to swing under the raised wheel truck


98


and railroad car


94


.




As shown in

FIG. 3

, the wheel handler assembly


10


is rotated or slewed to bring the grappler mechanism


64


to the inside of the gantry crane


12


. The handler assembly


10


is then trolleyed along the length of the lower side beam


26


via the connecting mechanism


80


, to bring the boom assembly


62


and grappler mechanism generally


64


in line with and adjacent to the wheel assembly


100


. That is, the double-ended hydraulic cylinder


84


is actuated to slide the assembly


10


along the length of the side beam


26


to the desired position.




From this general position, the wheel handler assembly


10


is manipulated to bring the lower stabilizing claws


92


into contact with the outside of the flange of the flanged wheel


102


. The upper locking claw


90


is then positioned to hook over the top of the flanged wheel


102


by contacting the inside surface of the flange of the flanged wheel


102


. This position can best be seen in

FIGS. 4 and 6

.




From this position, the wheel handling assembly


10


can lift the wheel assembly


100


, primarily through luffing. The first boom section


76


is then retracted so the wheel assembly


100


fully clears the wheel truck


98


. The handler


10


then traverses the lower side beam


26


until it is near the center of the lower side beam


27


. This is necessary to ensure that the wheel assembly


100


will not strike either right wheel


30


,


32


while it is being swung underneath the lower side beam


27


. The proximity switch


86


detects the position of the upper base portion


66


. The switch


86


will only allow the wheel handling assembly to swing the wheel assembly


100


under the side beam


27


if the upper base portion


66


is within a predetermined range of locations near the center of the side beam


27


thereby preventing the wheel assembly


100


from striking either wheel


30


,


32


. From this position, the wheel assembly


100


can be swung underneath the side beam


27


to the side and placed on the ground.




Once the old wheel assembly


100


has been set aside, the wheel handling assembly


10


is positioned near a new or replacement wheel assembly


100


located on the ground. The grappler mechanism


64


is positioned and manipulated as previously described to lock onto the new wheel assembly


100


which is then manipulated to be positioned on the track rails


99


underneath the raised wheel truck


98


. When properly positioned, the upper locking claw


90


is unhooked from the wheel assembly


100


, thereby releasing the same. The second boom section


78


is then fully retracted and the wheel handling assembly


10


is then swung out of the way. The load blocks


36


-


42


are operated to lower the spreader


44


ultimately lowering the railroad car


94


and wheel truck


98


. The traversing trolley


45


of the spreader


44


may be used to position the wheel truck


98


laterally with respect to the rails


99


to facilitate proper positioning. The wheel truck


98


is set on the new wheel assembly


100


. The proper attachments between the wheel assembly


100


and wheel truck


98


are then made completing the wheel assembly replacement.




Also, it is understood that the wheel handling assembly


10


can be adapted for attachment to structures in addition to gantry cranes. In additional embodiments, the wheel handling assembly


10


may be adapted for attachment to a stationary gantry crane, or other types of mobile or stationary cranes or lifting devices.




While the specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying Claims.



Claims
  • 1. A railroad car wheel changer assembly adapted to be mounted on a gantry crane, the assembly comprising:a base assembly adapted to be attached to a gantry crane: a beam member attached to the base assembly; and a grappler assembly, adapted to engage a railroad car wheel assembly, attached to a first end of the beam member; wherein the beam member is articulatable to move the wheel assembly.
  • 2. The assembly of claim 1 wherein the beam member comprises a telescoping boom assembly.
  • 3. The assembly of claim 2 wherein the telescoping boom assembly comprises:a first boom section pivotally attached to the base assembly; and a second boom section adapted to telescope within the first boom assembly; wherein the grappler assembly is attached to the second boom section.
  • 4. The assembly of claim 2 wherein the telescoping boom assembly comprises:a first boom section pivotally attached to the base assembly; a second boom section adapted to telescope within the first boom assembly; and a third boom section adapted to telescope within the second boom assembly; wherein the grappler assembly is attached to the second boom section.
  • 5. The assembly of claim 1 wherein the base assembly comprises:an upper base portion attached to the gantry crane; a lower base portion; and a slewing mechanism; wherein the beam member is attached to the lower base portion and the slewing mechanism rotationally connects the lower base portion to the upper base portion for rotational movement of the lower base portion with respect to the upper base portion in a generally horizontal plane.
  • 6. The assembly of claim 5 wherein the upper base portion is slidingly attached to the gantry crane via a connecting mechanism comprising:a track rail adapted to be attached to the gantry crane; a double ended hydraulic cylinder adapted to be attached to the gantry crane and attached to the upper base portion, the cylinder capable of sliding the upper base portion along a length of the track rail; and a proximity switch adapted to be connected to the gantry crane for detecting the location of the upper base portion.
  • 7. The assembly of claim 1 further comprising:a cylinder pivotally attached to both the base assembly and the beam member for rotating the beam member generally vertically about the base assembly.
  • 8. The assembly of claim 7 wherein the cylinder is attached to a second end of the beam member.
  • 9. A railroad car wheel changer assembly adapted to be mounted on a gantry crane, the assembly comprising:a base assembly adapted to be attached to a gantry crane: a beam member attached to the base assembly; a grappler assembly adapted to engage a railroad car wheel assembly, the grappler assembly being attached to a first end of the beam member; and means for articulating the beam member.
  • 10. The assembly of claim 9 wherein the base assembly comprises an upper base portion attached to the gantry crane and a lower base portion;wherein the means for articulating comprises a slewing mechanism for rotationally connecting the lower base portion to the upper base portion.
  • 11. The assembly of claim 9 wherein the means for articulating comprises a cylinder pivotally attached to both the base assembly and the beam member for rotating the beam member in a generally vertical plane.
  • 12. The assembly of claim 9 wherein the means for articulating comprises a telescoping boom assembly.
  • 13. A railroad car wheel changer assembly adapted to be mounted on a gantry crane, the assembly comprising:a base assembly adapted to be attached to the gantry crane; a telescoping boom assembly pivotally attached to the base assembly; and a grappler assembly, adapted to engage a railroad car wheel assembly, attached to a first end of the boom assembly; wherein the boom assembly is articulatable to move the wheel assembly.
  • 14. The assembly of claim 13 wherein the boom assembly rotates in a generally vertical plane.
  • 15. The assembly of claim 13 wherein the boom assembly rotates in a generally horizontal plane.
  • 16. The assembly of claim 13 further comprising:a cylinder pivotally attached to both the base assembly and to the boom assembly for rotating the boom assembly generally vertically about the base assembly.
  • 17. The assembly of claim 16 wherein the cylinder is attached to a second end of the boom assembly.
  • 18. The assembly of claim 13 wherein the base assembly is comprised of a rotating mechanism for rotating the boom assembly generally horizontally about the base assembly.
  • 19. The assembly of claim 13 wherein the grappler assembly further comprises:a plurality of grippers.
  • 20. The assembly of claim 13 wherein the grappler assembly further comprises:a locking clamp; and a plurality of stabilizing claws; wherein the locking clamp and the stabilizing claws cooperate to engage the wheel assembly.
  • 21. The assembly of claim 20 further comprising:a clamp cylinder pivotally attached to the locking clamp for moving the locking clamp between latched and unlatched positions.
  • 22. A railroad car wheel changer assembly adapted to be mounted on a gantry crane, the assembly comprising:a base assembly adapted to be attached to the gantry crane, the base having an upper portion connected to a lower portion by a slewing mechanism, and the base assembly further having a first hydraulic cylinder; a telescoping boom assembly pivotally attached to the lower portion and pivotally connected to the first hydraulic cylinder; and a grappler mechanism adapted to handle a railroad car wheel assembly, the mechanism being attached to the telescoping boom assembly and comprising a gripper and a second hydraulic cylinder pivotally attached to the telescoping boom assembly.
  • 23. A gantry crane comprising:a gantry structure; and a railroad car wheel changer comprising: a base assembly adapted to be attached to the gantry structure, the base having an upper portion connected to a lower portion by a slewing mechanism, and the base assembly further having a first hydraulic cylinder; a telescoping boom assembly pivotally attached to the lower portion and pivotally connected to the first hydraulic cylinder; and a grappler mechanism adapted to handle a railroad car wheel assembly, the mechanism being attached to the telescoping boom assembly and comprising a gripper and a second hydraulic cylinder pivotally attached to the telescoping boom assembly.
  • 24. A method of changing a railroad car wheel assembly attached to a wheel truck of a railroad car, comprising the steps of:providing a gantry crane having a railroad car wheel changer assembly attached thereto; positioning the gantry crane to straddle the railroad car; positioning the changer assembly to be adjacent the wheel assembly to be changed; unfixing the wheel assembly from the wheel truck; raising at least an end of the railroad car an adequate distance with the gantry crane to permit the wheel assembly to be moved underneath the truck; engaging the wheel assembly with the changer assembly; lifting the wheel assembly with the changer assembly; swinging the wheel assembly clear of the wheel truck; and disengaging the wheel assembly.
  • 25. The method of claim 24 further comprising the steps of:engaging a replacement wheel assembly with the changer assembly; swinging the replacement wheel assembly to a position underneath the wheel truck; lowering the railroad car with the gantry crane; affixing the replacement wheel assembly to the wheel truck; and disengaging the wheel assembly from the changer assembly.
US Referenced Citations (25)
Number Name Date Kind
1283656 Burke Nov 1918 A
1341501 Earley et al. May 1920 A
2053080 Henricks Sep 1936 A
2369838 Minnis Feb 1945 A
2370842 Christie Mar 1945 A
2451042 Nancarrow et al. Oct 1948 A
2505003 Perry et al. Apr 1950 A
2931519 Beach Apr 1960 A
2958508 Martinez Nov 1960 A
3161309 Baudhuin et al. Dec 1964 A
3176853 Baudhuin et al. Apr 1965 A
3251311 Saxonmeyer May 1966 A
3362351 Robertson Jan 1968 A
3744652 Rieschel Jul 1973 A
4068823 Belanger Jan 1978 A
4295427 Waterman et al. Oct 1981 A
4715762 Lanigan et al. Dec 1987 A
4747745 Pippen et al. May 1988 A
4805875 Jackson et al. Feb 1989 A
4903946 Stark Feb 1990 A
5133531 Grashoff et al. Jul 1992 A
5529452 Boyles et al. Jun 1996 A
5582451 Baumann Dec 1996 A
5876018 Crisp et al. Mar 1999 A
6158602 Zakula et al. Dec 2000 A