Step assembly with a removable step for hollow poles and the like

Information

  • Patent Grant
  • 6491272
  • Patent Number
    6,491,272
  • Date Filed
    Thursday, August 9, 2001
    23 years ago
  • Date Issued
    Tuesday, December 10, 2002
    21 years ago
Abstract
There is provided a pole step assembly with a removable step for hollow poles and the like. The step assembly includes a mounting subassembly with a mounting stud and a mounting plate with inter-engaging flat surfaces that limit relative rotational movement of the mounting stud and mounting plate about the axis of the subassembly. A clamp is provided to limit radial movement of the subassembly relative to the pole. The mounting stud of the subassembly also may include a handle portion that captivates the components of the subassembly and facilitates ease of installation of the subassembly. The handle also may break away and be removed after installation of the subassembly. The step is mounted to the subassembly and may include flat surfaces that inter-engage with further flat surfaces on the mounting plate to limit rotation of the step about its longitudinal axis.
Description




FIELD OF THE INVENTION




The present invention relates generally to steps for climbing hollow poles, such as utility poles, and similar structures and, more particularly, to a pole step assembly with a mounting subassembly that can be attached to such structures and a removable step that can be readily attached and detached from the mounting subassembly.




BACKGROUND OF THE INVENTION




Elongated poles are commonly used to maintain items above and over the ground for numerous reasons, including safety and ground space conservation purposes. The utility industry, for example, uses many poles to support cables and other components of the utility's system. These poles are often hollow and made of steel and/or fiberglass. These poles are typically fitted with steps that extend radially from the pole in a cantilever fashion to enable utility personnel to climb the pole to perform maintenance operations on the equipment. The specific structures of these pole steps vary.




In a number of instances, there is also a desire for an effective but easily removable step. This is especially the case for the lower portion of poles to prevent unauthorized climbing of the poles. There exists pole step assemblies with detachable steps. A known shortcoming with these assemblies is the lack of adequate protection against unwanted rotation of the step about its longitudinal axis created by a user's foot rubbing across the step or hitting the step from underneath.




The related application, Ser. No. 09/757,296, U.S. Pat. No. 6,378,822 B1 provides a pole step assembly that secures the step against unintentional rotational movement and facilitates efficient and effective installation to the pole by preventing the loss of necessary components. Although this pole step assembly is considered removable, there, however, is a need for additional features to further facilitate removability of the step.




Thus, there remains a need for a pole step assembly that secures the step against unintentional rotational movement and that facilitates efficient and effective installation to the pole by preventing the loss of necessary components. Furthermore, it would be advantageous if the assembly included a mounting subassembly and a removable step so that the step could be easily attached and detached from the pole while the mounting subassembly remained permanently affixed thereto.




SUMMARY OF THE INVENTION




The present invention pertains to a removable pole step assembly that includes a mounting subassembly and a removable step that can be readily attached and detached thereto. A step assembly in accordance with the present invention is capable of selectively securing a removable step to a hollow pole with a mounting aperture.




The assembly includes a mounting stud with a first portion and a second portion. The first portion is capable of engaging the hollow pole to support the mounting stud.




The second portion has an exterior flat portion that is capable of extending through the aperture in the hollow pole to position the first portion inside the hollow pole. A mounting plate is on the stud and has an interior surface with a flat portion to engage the exterior flat portion of the second portion of the mounting stud to limit relative movement between the mounting plate and the mounting stud. The mounting plate also has a major exterior surface and a minor exterior surface. The major exterior surface is stepped from the minor exterior surface such that the major exterior surface is capable of engaging the hollow pole and a gap forms between the minor surface and the hollow pole when the major surface engages the hollow pole. The major surface has at least a portion profiled so when it is engaged with the hollow pole it limits movement between the hollow pole and the mounting plate.




A clamp is on the mounting stud and is capable of selectively engaging the second portion of the mounting stud to secure the mounting plate and the first portion of the stud into engagement with the hollow pole to limit relative movement of the mounting plate and mounting stud with respect to the hollow pole. A removable step has a mounting portion and a foot support portion. The mounting portion defines a slot and is capable of a being received in the gap to engage at least a portion of the minor surface and surround at least a portion of the major surface to limit movement of the step relative to the hollow pole when the mounting plate is in engagement with the pole.




The mounting stud may further include a handle to facilitate installation of the mounting stud and mounting plate. The handle may also be removably attached to the mounting stud. Additionally, the handle may have an enlarged end portion to maintain the mounting plate and clamp on the mounting stud.




Further, the second portion of the mounting stud may define a recess and the handle may have a mounting end that is press fit into the recess to attach the handle. Even further, the handle may have a weaker portion that is capable of being severed to remove the handle when desired, and the enlarged end portion may be C-shaped.




The first portion and the second portion of the mounting stud may be disposed at a predetermined angle relative to one another. The predetermined angle may be generally 90 degrees so that the second portion is capable of extending in a direction that is generally parallel to the radius of the hollow pole.




The major surface of the mounting plate may have an arcuate profiled portion so when it is engaged with the hollow pole it limits movement between the hollow pole and the mounting plate.




The second portion of the pole step stud may have an externally threaded portion. The clamp may include a nut that meshes with the externally threaded portion of the second portion of the mounting stud. The clamp may further include a lock washer interposed between the nut and the mounting plate.




The mounting stud may be sized large enough to prevent the mounting plate and clamp from falling off the mounting stud at the first portion. The exterior flat portion of the second portion of the mounting stud may include at least two flats and the flat portion of the interior surface of the mounting plate may include at least two flats. The flats of the second portion and the interior surface then are capable of engaging each other to limit relative movement between the mounting plate and the mounting stud.




There is also provided a method of attaching a removable pole step assembly to a hollow pole. The method includes the step of providing a removable pole step assembly having a mounting subassembly with a removable handle. The mounting subassembly is attached to the hollow pole, and after such attachment the removable handle is detached. The final step is to attach a removable step to the mounting subassembly.











DESCRIPTION OF THE DRAWINGS





FIG. 1

is a perspective view of an installed pole step assembly with a removable step in accordance with the present invention;





FIG. 2

is an exploded, perspective view of the pole step assembly of

FIG. 1

before installation;





FIG. 3

is a side cross-sectional view of the mounting subassembly of the pole step assembly of

FIG. 2

partially installed;





FIG. 4

is a side cross-sectional view of the mounting subassembly of

FIG. 3

after being installed;





FIG. 5

is a side cross-sectional view of the removable step assembly of

FIG. 1

, taken along line


5





5


of FIG


1


;





FIG. 6

is a front elevational view of the mounting plate of the mounting subassembly of the pole step assembly of

FIG. 2

;





FIG. 7

is a right side elevational view of the mounting plate of

FIG. 6

;





FIG. 8

is a top view of the mounting plate of

FIG. 7

;





FIG. 9

is a cross-sectional view of the mounting plate of taken along line


9





9


of

FIG. 6

;





FIG. 10

is a side elevational view of the removable step of the pole step assembly of

FIG. 2

; and





FIG. 11

is a front elevational view of the removable step of FIG.


10


.











DESCRIPTION OF THE PREFERRED EMBODIMENT




Referring to

FIGS. 1 and 2

, the present invention is embodied in a pole step assembly that includes a mounting subassembly


20


for a removable step


22


that can be readily attached and detached to a hollow pole


24


. The mounting subassembly


20


includes a number of inter-engaging surfaces designed to prevent unintentional movement of the step assembly relative to the pole, such as that design also disclosed in the related patent U.S. Pat. No. 6,378,822 B1 which is incorporated by reference herein.




The mounting subassembly


20


includes a pole step stud


26


, a mounting plate


28


, a clamp


30


and a break away handle


32


. The pole step stud


26


and break away handle


32


are shaped and sized to captivate the components of the mounting assembly, such as the mounting plate


28


and components of the clamp


30


, into a single assembly, thereby rendering it easier for the user to install the subassembly


20


, because there is no additional concerns from potentially dropping or losing necessary components. Once the mounting subassembly


20


has been installed, it is designed to remain in position at the pole


24


while the removable step


22


can be readily attached to (as well as detached from) the mounting subassembly


20


after the break away handle


32


has been removed after installation.




Referring to

FIGS. 2-5

, the pole step stud


26


includes a first portion


34


and a second portion


36


disposed at an angle to the first portion


34


. The first and second portions


34


and


36


are separated by a bend portion


37


. For example, the preferred angle of the bend sets the first and second portions


34


and


36


at an angle of about 90 degrees. The preferred radius of curvature for the bend may be 0.133±0.010 inches.




The first portion


34


is designed to engage the interior surface


48


of the pole


24


adjacent the bore


38


. The first portion


34


includes a square cross-section providing four outer flat surfaces


39




a-d


To ensure that the components of the assembly remain together, and to cooperate with the bore


38


, the cross-sectional dimension may be in the range of about 0.750±0.010 inches. The first portion


34


may also be long enough to provide a sufficient amount of engagement with the interior


48


of the pole


24


to provide a predetermined amount of support. For example, the preferred length of engagement is about 1.528±0.010 inches.




Alternatively, the first portion


34


can have a circular cross-section with a round outer surface. For example, the cross-sectional diameter may be in the range of about 0.750±0.010 inches, and the length of engagement maybe about 1.578±0.010 inches.




The second portion


36


of the pole step stud


26


includes a first segment


40


with a square cross-section providing four outer flat surface


42




a-d


(note that due to the orientation of the Figures only


42




a


and


42




c


are visible) and a second segment


43


threaded to cooperate with a nut


60


, as explained herein. The cross-sectional dimension may be in the range of about 0.750±0.010 inches, and the threads may be ¾-10 UNC-620. The second portion


36


also may be long enough to extend through the bore


38


to position the first portion


34


in the pole


24


. For example, the first segment


40


may be 0.750±0.010, and the second segment


43


may be 0.620.




The pole step stud


26


is to be made from any material that provides sufficient strength for supporting the user and durability to withstand being in an outside environment. Appropriate materials include 430 stainless steel and may have a light zinc electroplating.




As illustrated in

FIGS. 3 and 4

, the mounting subassembly


20


easily attaches to the hollow pole


24


. That is, the break away handle


32


is used to first rotate the first portion


34


of the pole step stud


26


through the bore


38


defined by the circumferential wall


46


of the hollow pole


24


until the first portion


34


is positioned inside the pole


24


and in engagement with the inside surface


48


of the hollow pole


24


. Next, the handle


32


is turned to orient the first portion


34


to point upwards in a generally vertical direction. It is preferred that the first portion


34


be aligned generally parallel with the longitudinal axis of the pole


24


.




Alternatively, the second portion can have an additional segment, thus three segments. More specifically, there may be a first segment nearest the first portion with a circular cross-section, a second segment adjacent the first with a square cross-section and a third threaded to cooperate with the nut. The first segment is designed to extend through the hole in the pole. The flat surfaces of the second segment are designed to interengage with the mounting plate to limit movement. The circular cross-section diameter may be about 0.750±0.010 inches, the square cross-section dimension may be about 0.750±0.005 inches and the threads may be ¾-10 UNC-2A. The first segment may have a length of 0.260±0.010 inches, the second segment may have a length of about 1.248±0.010 inches, and the third segment may have a length of about 0.620±0.010 inches.




The mounting plate


28


is designed to engage the exterior of the hollow pole


24


and the second portion


36


of the pole step stud


26


to prevent relative movement between these components and movement relative to the pole


24


. More specifically, as illustrated in

FIGS. 6 and 9

, the plate


28


includes four interior edges


49




a-d


that define a hole


50


through which the second portion


46


of the pole step stud


26


extends. The hole


50


is located generally in the center of the plate


28


and has a square cross-section that compliments the outer flat surfaces


42


of the second portion


36


of the pole step stud


26


. That is, each of the edges


49


has a flat surface


52




a


-


d


designed to engage one of the four flat exterior surfaces


42




a


-


42




d


of the second portion


36


to prevent relative rotational movement between the plate


28


and the stud


24


after installation of the mounting subassembly


20


. For example, the cross-section dimension of the hole may be 0.760±0.010 inches.




The rear side


53


of the mounting plate


28


includes a center portion


54


about the hole


50


that is stepped away from the periphery portion


55


of the rear side


53


. This center portion


54


spaces the periphery portion


55


of the rear side


53


from the mounting plate


28


for attachment of the removable step


22


, as described infra. The center portion


54


includes an arcuate surface


56


to complement that of the exterior


46


of the pole


24


to prevent relative movement between the plate


28


and the pole


24


. The arcuate surface


56


may have a radius of curvature of about 5.0 inches.




While holding the pole step stud


26


with the handle


32


to maintain the first portion


34


against the interior


48


of the pole


24


, the user orients the mounting plate


28


until it is vertical and its internal flats


52


mate with the external flats


42


of the second portion


36


of the pole step stud


26


. Then, the user pushes on the mounting plate


28


toward the pole


24


until the arcuate surface


56


of the mounting plate


28


engages the exterior surface


46


of the hollow pole


24


. As a result, the mounting plate


28


will not rotate with respect to the pole


24


because of the engagement of the arcuate surface


56


to the pole


24


nor will the pole step stud


26


rotate with respect to the mounting plate


28


because of the engagement of the flats


52


of the interior hole


50


of the mounting plate


28


to the external flats


42


of the second portion


46


of the pole step stud


26


once the clamp


30


has been secured. Hence, the removable pole step is prevented from unintentionally rotating, due to some torque that may be provided either by a climber or some other external influence, which would result in having the first portion


34


of the pole step stud


26


no longer facing upwards, but in some other less desirable position.




The next step is for the user to tighten the clamp


30


until the mounting subassembly


20


is secured to the pole


24


. The clamp


30


preferably comprises a locking washer


58


and a nut


60


, so the user would first slide the locking washer


58


until it is flush with mounting plate


28


and then rotate the nut


60


until it engages the threads


62


of the second segment


43


of the second portion


36


of the pole step stud


26


. Preferably, the internal threads


64


of the nut


60


and the external threads


62


of the second portion


36


of the pole step stud


26


would be of the ¾-10 UNC-2A variety to ensure that sufficient clamp force is generated. The locking washer


58


further ensures that the nut


60


will not become loose due to vibration.




After the nut


60


has been tightened, then the break away handle


32


is removed by severing its attachment to the second portion


36


of the pole step stud


26


because the purpose of the handle


32


is to prevent the mounting plate


28


, locking washer


58


, and nut


60


from falling off the mounting subassembly


20


before it has been secured to the pole


24


, thereby facilitating installation and to provide a useful mechanism to grip, orient and otherwise manipulate the mounting subassembly


20


for installation.




The handle can be of any Shape. For example, the handle


32


can have a C-shaped curl


66


that is located at its end that is opposite to its attachment to the second portion


36


of the pole step stud


26


. The handle


32


is of sufficient size and shape to prevent the other components from falling off the mounting subassembly


20


. The handle


32


is removed before attaching the removable step


22


to the mounting subassembly


20


because the C-shaped curl


66


could interfere with the underside of the removable step


22


.




The break away handle


32


is attached to the free end of the second portion


36


of the pole step stud


26


with a press fit friction engagement. More specifically, the free end


68


of the second portion


36


defines a centrally located hole


70


about the center axis of the second portion


36


. A knurled knob


72


formed on the end of the handle


32


is press fit into the hole


70


. A thin neck potion


74


is formed between the remainder of the handle


32


and the knob


72


.




Preferably, the knob


72


has a diameter that is 0.009±0.010 of an inch larger than the press fit hole


70


, as well as a twenty-four pitch straight knurl on its circumferential surface to make sure that there is sufficient interference to retain the knob


72


within the hole


70


. For example, the diameter of the hole maybe 0.250±0.010 inches and the outer diameter of the knob


72


after knurling may be 0.259±0.010 inches.




In addition, the thin neck portion


74


should not be so long that it breaks during assembly or installation of the subassembly


20


. For example, it is preferred that the thin neck


74


be about 0.093±0.010 inches in diameter and 0.125±0.010 inches long to make sure that the break away handle


32


will not be severed from the mounting subassembly


20


unintentionally but only when purposely pushed on by the user after the mounting subassembly


20


has been attached to the pole


24


, causing the thin neck


74


to fracture.




The break away handle


32


may be made of any suitable material that provides sufficient durability, including metal, such as C.R.S. zinc plated.




The final step of installation would be mounting of the removable step


22


by way of the mounting subassembly


20


. As shown in

FIG. 4

, a gap


94


forms between the periphery portion


55


of the rear side


53


about the center portion


54


of the mounting plate


28


and the exterior


46


of the pole


24


. This gap


94


receives a wall portion


80


of the removable step


22


, as described infra. A front side


76


of the mounting plate


28


includes a cup-like shape defined by a flange


78


extending about the top and sides of its perimeter to provide strength.




More specifically, as illustrated in

FIGS. 5

,


10


and


11


, the front wall


80


of the removable step


22


is designed to attach the step


22


to the mounting subassembly


20


. More specifically, the front wall


80


defines a slot


82


that opens downward. The slot


82


has a squared U-shape with a top straight edge


84


and a pair of generally parallel side edges


88


that form generally right angles with the top edge


90


. The size of the slot


80


is designed to complement the perimeter of the center portion


54


of the mounting plate


28


of the mounting subassembly


20


.




To mount the step


22


, the slot


82


is slid downward over the center portion


54


until the top edge


84


of the slot


82


bottoms out on a top side


86


of the center portion


54


. The side edges


88


of the slot


82


engage sides


90


of the center portion


54


to limit lateral movement of the step


22


relative to the center portion


54


. Consequently, to detach the removable step


22


, the step


22


is lifted upward until the wall


80


and the slot


82


are moved clear of the mounting plate


28


.




The thickness


92


of the front wall


80


is coordinated to complement the width of the gap


94


between the periphery portion


55


of the rear side


53


of the mounting plate


28


about the center portion


54


and the exterior surface


46


of the hollow pole


24


. This minimal clearance aids in securing the step to the mounting subassembly


20


because it is pinched between the mounting plate


28


and the pole


24


.




The gap between the exterior surface


38


of the pole


24


and the periphery portion


55


of the mounting plate


28


may have a width of about 0.125±0.010 inches and the front wall


80


may have a thickness of about 0.093±0.010 inches. Thus, the preferred clearance is about 0.032±0.010 inches.




The same clearance is preferred between the side edges


88


of the slot


82


and the side


90


of the center portion


54


. For example, the center portion


54


may have its sides


90


spaced apart about 1.200±0.010 inches and the side edges


88


of the slot


82


may be spaced apart about 1.265±0.010 inches. Thus, the clearance at each edge pair is about 0.032±0.010 inches.




In addition, the engagement between the straight edges


88


of the slot


82


and the straight perimeter sides


90


of the center portion


54


prevent rotational movement of the step


22


relative to the mounting plate


28


and the pole


24


. Further the side edges


88


of the slot


82


may be rounded at the opening to provide guidance of the slot


82


around the center portion


54


to further aid in attaching the step


22


.




The top wall


95


has a front portion with a lip


96


, a stop


98


at its other end and a step portion


100


for a user's foot extending between the lip


96


and the stop


98


. The lip


84


projects above the step portion


100


and defines an interior portion that receives the upper edge of the mounting plate


28


. That is, the lip


96


wraps over the upper edge of the mounting plate


28


to further aid in securing the step


22


to the mounting subassembly


20


.




The step portion


100


includes a tread


102


to enhance the footing of the users. The tread


102


can be in the form of raised dimples or other shapes stamped in the step portion


100


. The step portion


100


tapers as it proceeds to the stop


98


. The stop


98


hooks upward. and aids to prevent the user's foot from sliding off the end of the step


22


.




The step


22


includes side walls


104


extending downwards from the step portion


100


of the top wall


95


and rearward from the front wall


80


. The side walls


104


taper upward toward the stop


98


. The side walls


104


are generally at right angles to the top wall


95


and the front wall


80


to provide support for the step portion


22


.




The preferred step is approximately 5.825±0.010 inches in length to provide adequate room for a user's foot. The step may also by made from any suitable material that provides sufficient strength to support a user. For example, the material can be 0.93 inch thick cold roll galvanized steel.




While the invention has been described in the specification and illustrated in the drawings with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is not intended that. the invention be limited to the particular embodiments illustrated by the drawings and described in the specification as the best modes presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the description of the appended claims.



Claims
  • 1. A step assembly that is capable of selectively securing a removable step to a hollow pole, the hollow pole being adapted to define at least one mounting aperture, the assembly comprising:a mounting stud having a first portion and a second portion, the first portion being capable of engaging the hollow pole to support the mounting stud, the second portion having an exterior flat portion and being capable of extending through an aperture in the hollow pole to position the first portion inside the hollow pole; a mounting plate on the stud having an interior surface with a flat portion to engage the exterior flat portion of the second portion of the mounting stud to limit relative movement between the mounting plate and the mounting stud, a major exterior surface and a minor exterior surface, the major exterior surface being stepped from the minor exterior surface such that the major exterior surface is capable of engaging the hollow pole and a gap forms between the minor exterior surface and the hollow pole when the major surface engages the hollow pole, the major exterior surface having at least a portion profiled so when it is engaged with the hollow pole it limits movement between the hollow pole and the mounting plate; a clamp on the mounting stud and being capable of selectively engaging the second portion of the mounting stud to secure the mounting plate and the first portion of the stud into engagement with the hollow pole to limit relative movement of the mounting plate and mounting stud with respect to the hollow pole; and a removable step having a mounting portion and a foot support portion, the mounting portion defining a slot, the mounting portion being capable of a being received in the gap to engage at least a portion of the minor exterior surface surround at least a portion of the major surface to limit movement of the step relative to the hollow pole when the mounting plate is in engagement with the pole.
  • 2. The pole step assembly of claim 1 wherein the mounting stud further includes a handle to facilitate installation of the mounting stud and mounting plate.
  • 3. The pole step assembly of claim 2 wherein the handle is removably attached to the mounting stud.
  • 4. The pole step assembly of claim 3 wherein the handle has an enlarged end portion to maintain the mounting plate and clamp on the mounting stud.
  • 5. The pole step assembly of claim 4 wherein the second portion of the mounting stud defines a recess and wherein the handle has a mounting end that is press fit into the recess to attach the handle.
  • 6. The pole step assembly of claim 5 wherein the handle has a weaker portion that is capable of being severed to remove the handle when desired.
  • 7. The pole step assembly of claim 6 wherein the enlarged end portion of the handle has C-shape.
  • 8. The pole step assembly of claim 1 wherein the first portion and the second portion of the mounting stud are disposed at a predetermined angle relative to one another.
  • 9. The pole step assembly of claim 8 wherein the predetermined angle between the first portion and second portion of the mounting stud is generally 90 degrees so that the second portion is capable of extending in a direction that is generally parallel to the radius of the hollow pole.
  • 10. The removable step assembly of claim 8 wherein the major exterior surface of the mounting plate has an arcuate profiled portion so when it the mounting stud is engaged with the hollow pole movement is limited between the hollow pole and the mounting plate.
  • 11. The pole step assembly of claim 8 wherein the second portion of the mounting stud has an externally threaded portion.
  • 12. The pole step assembly of claim 11 wherein the clamp further comprises a nut that meshes with the externally threaded portion of the second portion of the mounting stud.
  • 13. The pole step assembly of claim 12 wherein the clamp further comprises a lock washer interposed between the nut and the mounting plate.
  • 14. The pole step assembly of claim 8 wherein the first portion of the mounting stud is sized large enough to prevent the mounting plate and clamp from falling off the mounting stud at the first portion.
  • 15. The pole step assembly of claim 8 wherein the exterior flat portion of the second portion of the mounting stud includes at least two flats and the flat portion of the interior surface of the mounting plate includes at least two flats, the flats of the second portion and of the interior surface being capable of engaging each other to limit relative movement between the mounting plate and the mounting stud.
  • 16. The method of attaching a removable pole step assembly to a hollow pole comprising:providing a removable pole step assembly having a mounting subassembly with a removable handle; attaching the mounting subassembly to a hollow pole; detaching the removable handle once the mounting subassembly has been attached to the hollow pole; and attaching a removable step to the mounting subassembly.
CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 09/757,296, filed on Jan. 9, 2001 now Pat. No. 6,378,822 B1 and entitled “STEP ASSEMBLY FOR HOLLOW POLES AND THE LIKE”.

US Referenced Citations (6)
Number Name Date Kind
1322869 Benedict Nov 1919 A
1588566 Wismer Jun 1926 A
1740873 Peirce, Jr. Dec 1929 A
5279388 Laughlin et al. Jan 1994 A
5761875 Oliphant et al. Jun 1998 A
5941485 Davidson et al. Aug 1999 A
Continuation in Parts (1)
Number Date Country
Parent 09/757296 Jan 2001 US
Child 09/925855 US