TIMBER ACCESS MAT WITH GROUNDING

Abstract

A timber access mat having an electrical grounding feature includes an electrically conductive cover layer that is removably carried over the top of the body of the timber access mat. The electrically conductive cover layer can be formed from one or more sheets of expanded metal such as expanded steel. The layer is joined to a perimeter frame that includes offset connector tabs that allow mats to be positioned side-by-side. The connector tabs are paired with cable guides to protect the cable leads that connect the mats. The perimeter frame and conductive cover layer can be added to traditional timber access mats when electrical grounding is required and then removed and stored when not required.

Claims

1. A timber access mat with an electrical grounding feature; the mat comprising: a mat body having an upper perimeter edge; a metal frame disposed around the upper perimeter edge of the mat body; metal connector tabs extending outwardly from the metal frame; the metal connector tabs being disposed in complementary positions on opposite sides of the metal frame; the complementary positions of the metal connector tabs adapted to allow a pair of timber access mats being placed side-by-side without the metal connector tabs interfering with each other; and a conductive cover layer being connected to the metal frame and disposed over the mat body.

2. The timber access mat of claim 1, further comprising a cable guide connected to the frame; the cable guide defining an opening.

3. The timber access mat of claim 2, further comprising a flexible electrical cable lead connected to one of the metal connector tabs; the flexible electrical cable lead extending through the cable guide.

4. The timber access mat of claim 1, wherein the frame defines four sides and four corners; a cable guide being disposed between each corner and one of the metal connector tabs; each of the cable guides defining an opening.

5. The timber access mat of claim 4, further comprising a flexible electrical cable lead connected to each of the connector tabs; each of the flexible electrical cable leads extending through one of the cable guides.

6. The timber access mat of claim 1, further comprising a flexible electrical cable lead connected to one of the metal connector tabs; the flexible electrical cable lead having an end disposed parallel to the portion of the frame from which the connector tab extends.

7. The timber access mat of claim 6, wherein the end of the flexible electrical cable is disposed on top of the connector tab.

8. The timber access mat of claim 7, wherein the end of the flexible electrical cable is connected to the connector tab with a threaded connector.

9. The timber access mat of claim 8, wherein the connector tab defines a threaded opening that receives the threaded connector.

10. The timber access mat of claim 8, wherein a threaded nut is connected to the connector tab and receives the threaded connector.

11. The timber access mat of claim 7, wherein the end of the flexible electrical cable is connected to the connector tab with a pair of spaced bolts.

12. The timber access mat of claim 1, further comprising a grounding pin connected to the frame.

13. The timber access mat of claim 1, wherein the conductive cover layer is formed from an expanded steel.

14. The timber access mat of claim 13, further comprising connectors removably connecting the conductive cover layer to the mat body.

15. The timber access mat of claim 14, wherein the connectors include lag bolts that extend into the mat body.

16. The timber access mat of claim 13 wherein outer edges of the conductive cover layer are disposed under the metal frame.

17. The timber access mat of claim 16, wherein the connectors include lag bolts that extend through the metal frame, through the conductive cover layer, and into the mat body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 depicts a top view of one configuration of the grounded timber access mat.

[0015] FIG. 2 is a perspective view of the FIG. 1 configuration.

[0016] FIG. 3 is a top view of a second configuration the grounded timber access mat.

[0017] FIG. 4 is a top plan view of a four timber access mats arranged in an array.

[0018] FIG. 5 is a top plan view of a single grounded timber access mat according to the third configuration.

[0019] FIG. 6 is a side view taken along line 6-6 of FIG. 5.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0020] In the configuration of FIGS. 1 and 2, a timber access mat 2 includes a plurality of non-conductive mat body members 4 disposed within a metal perimeter frame 6 disposed around the outside of the combined body members 4. Metal grounding slats 8 are disposed between or on top of body members 4. The ends of each metal grounding slat 8 are connected to perimeter frame 6. The ends can abut frame 6, rest on top of frame 6, or be disposed under frame 6. Each metal grounding slat 8 extends at least slightly above the upper surface of body members 4 so that a vehicle, a person, or other equipment supported by mat 2 will be in contact with at least one metal grounding slat 8. FIG. 2 depicts the raised nature of metal grounding slats 8 in an exaggerated manner. Each metal grounding slat 8 can extend about a quarter inch above the upper surface of body members 4. Slats 8 can be a quarter inch by a quarter inch metal strips disposed on top of body members 4. When body members 4 are traditional 24, 26, or 28 lumber, there can be multiple metal grounding slats 8 disposed on each body member 4. Limiting the distance between metal grounding slats 8 provides that a person or a vehicle will be in contact with at least one of metal grounding slats 8 when the person or vehicle is supported by timber access mat 2. A distance of four to six inches from edge to edge between adjacent metal grounding slats 8 is disclosed. Cross slats (not shown) can be used to increase the coverage of the conductive grounding members. The cross slats can be perpendicular to slats 8. Each of metal grounding slats 8 can be disposed one quarter of an inch above the upper surface of body members 4. Metal grounding slats 8 can be friction fit to frame 6, bolted or riveted to frame 6, or welded to frame 6.

[0021] An alternative configuration uses a filler material or a filler strip disposed between slats 8 to provide a flat surface to mat 2.

[0022] Flexible electrical cable leads 10 are connected to frame 6. Cable leads 10 can be located near the corners of frame 6. A pair or a plurality of cable leads 10 can extend from each location. Cable leads 10 are used to connect mats 2 or connect mat 2 to a grounding pin that is driven into the ground. Cable leads 10 can be bolted to frame 6 but also can be welded to frame 6. Each cable lead 10 can carry a bolt receiver at its loose end for receiving a bolt that is used to secure cable lead 10 to another mat 2 or to the grounding pin.

[0023] The mat configurations of FIGS. 3-6 are similar to the above configuration and the same reference numerals are used to identify similar elements. In place of slats 8, these mat configurations use a conductive cover layer 12 that is in the form of a mesh or conductive screen made of electrically conductive material such as steel. Another configuration uses a thin perforated metal foil as the conductive cover layer 12. One or a plurality of expanded metal sheets can be used over the body of the mat as conductive cover layer 12. An advantage to using the mesh, screen, or expanded metal is that the size of the gaps between conductive elements is small and a person standing on mat 2 is guaranteed to be in contact with multiple locations of layer 12. Conductive cover layer 12 can be bolted or welded to frame 6. Conductive cover layer 12 also can be wrapped around the sides of frame 6 and bolted to the sides or bottom of frame 6.

[0024] In the configurations using expanded metal sheets as conductive cover layer 12, each sheet of expanded metal can be lag bolted down into the body members of the mat with washers cooperating with the bolt heads to grip the expanded metal sheet. The lag bolts and washers allow the expanded metal layer 12 and frame 6 to be to and removed from the body members 4. This allows existing non-grounding timber access mats to be converted to grounding mats as needed. The edges of adjacent expanded metal sheets 12 are overlapped and either secured with bolts or welds or left loose. The expanded metal sheets 12 are welded or bolted to frame 6. An upper leg of frame 6 extends over an upper perimeter portion of the body with the edges of the expanded metal sheets disposed under the upper leg of frame 6. Another leg of frame 6 extends down the side of the body of the mat. The two legs cooperate to define an L-shaped cross section such that frame 6 sits over and surrounds the upper corners of the mat body. The upper leg of frame 6 is secured with connectors such as lag bolts directly down into the body members of the mat.

[0025] The grounding pin 18 is connected to frame 6 with a flexible cable 10. The flexible cable is connected at a raised U or C-shaped cleat that allows a tight bolted connection to be made between the flexible cable 10 and the frame 6. A plurality of flexible cables 10 can extend from a single cleat. The flexible cables 10 allow multiple mats to be electrically connected to a single grounding pin 18.

[0026] This configuration of FIG. 3 also discloses the use of flexible connectors 14 disposed under cover 12 and between body members 4 to directly connect the different locations where cable leads 10 are secured to frame 6 in order to provide for direct cabled electrical contact between these locations. Connectors 14 may be disposed between body members 4 and lower than the upper surface of body members 4. Connectors 14 can be directly connected to the inside of frame 6 or wrapped under the lower edge of frame 6 and connected to the cleats the receive cable leads 10.

[0027] A filler material can be used to fill the openings defined by the material of cover 12. The filler can be a rubber or polymer material that is sprayed onto the top of mat 2 in an amount thin enough to leave the upper surfaces of cover 12 exposed.

[0028] In the configuration of FIGS. 4-6, a timber access mat 20 includes a plurality of body members 4 disposed within a metal perimeter frame 6. Frame 6 includes four upper, generally horizontal, frame members disposed over the outer upper perimeter portions of the timber access mat body. Frame 6 also includes vertical frame members extending down from the outer edges of the upper frame members such that they are disposed outwardly or against the outside edges of the timber access mat body. Conductive cover layer 12 such as a sheet or multiple sheets of expanded metal are disposed over the top of body members 4 with the perimeter edges of the expanded metal sheets disposed under the upper frame members of frame 6 as depicted in FIG. 4. The conductive cover layer 12 can be welded to frame 6. Also, bolts 22 may be used to secure the perimeter edge of conductive cover layer 12 to frame 6. In some configurations, bolts 22 do not extend into body members 4. In other configurations, bolts 22 are lag bolts that extend through frame 6, through conductive cover layer 12, and into body members 4 to removably secure the assembly together. Bolt and washer combinations 24 can be used to connect the expanded metal sheets to body members 4. The washers can be integrated with bolts or provided as separate articles. Bolts 22 and 24 can be removed to allow frame 6 and cover layer 12 to be removed from body members 4.

[0029] A plurality of connector tabs 30 extend from the vertical walls 32 of frame 6. Connector tabs 30 extend generally horizontal from vertical walls 32. Connector tabs 30 can be formed by welding or securing with mechanical connectors L-shaped lengths of metal to the outer side surfaces of frame 6. Connector tabs 30 are arranged in complementary positions on opposite walls of frame 6 such that mats 20 can be arranged side-by-side without connector tabs 30 interfering with each other. FIG. 5 shows how connector tabs 30 are offset so they interlock and FIG. 4 depicts how these positions complement each other. Connector tabs 30 may directly abut the other frame 6 or cable guides 34 may directly abut the other frame or both can be the same width and function to space the adjacent frame members and prevent the crushing of cable leads 10. Each cable guide 34 is a loop sized to receive cable leads 10. Threading cable leads 10 through cable guide 34 helps prevent cable lead 10 from being pinched between adjacent mats 20 and prevents cable from falling down below the mats. In this configuration, each cable lead 10 is secured to connector tab 30 with a pair of bolts 36 that position the end of cable lead 10 parallel (and substantially horizontal) to the wall of frame 6 from which connector tab 30 extends. This keeps the ends of cable leads 10 out of the way when mats 20 are disposed edge-to-edge. Each connector tab can define space for multiple cable lead ends. Bolts 36 can be threaded into threaded openings 38 (FIG. 6) or into threaded nuts (optional) 40 welded to the bottom of connector tab 30. This configuration allows bolts 36 to be secured when mats 20 are disposed edge-to-edge as shown in FIG. 4. Cable leads 10 are used to electrically connect mats 20. Cable leads 10 also are used to connect a grounding pin to mat 20.

[0030] The metal frame 6 and conductive cover layer 12 can be galvanized.

[0031] In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. Moreover, the descriptions and illustrations of the exemplary configurations are examples and the claimed invention is not limited to the exact details shown or described. Throughout the description and claims of this specification the words comprise and include as well as variations of those words, such as comprises, includes, comprising, and including are not intended to exclude additives, components, integers, or steps.