Abstract:
A laminated treadmill deck insert includes a wear surface formed of a phenolic impregnated paper laminated to an isocyanate resin bonded MDF insert core less than about 5/16 inch thick. A low moisture content isocyanate resin bonded wood fiber MDF core enables dimensional stability and high internal bonding strength even at reduced insert thicknesses. The deck insert is disposed on a support deck adjacent the upper run of an endless treadmill belt. The insert is provided with wear surfaces on each broad side and is easily removable and reversible to expose the second wear surface.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to treadmills, in particular to low friction treadmill decks. 
       BACKGROUND 
       [0002]    A treadmill is a common exercise device designed to enable walking or running on an endless belt. The belt is trained about a set of rollers, which are powered at different speeds by a motor. The belt is tensioned between the rollers and is supported by a low friction deck extending between the rollers. The rollers, motor and deck are all supported by a rigid frame. Treadmills also commonly include user support handles, control panels and tilt mechanisms. 
         [0003]    Treadmill decks generally include a plywood panel or other natural or synthetic fiber panel coated or impregnated with wax, plastic resin or other low friction material. Such decks are commonly a monolithic structure that provides both the structural support for the weight of the user and the low friction wear surface to allow movement of the belt across the deck even during the impulse friction from the user&#39;s footsteps. 
         [0004]    Some existing belt and treadmill deck combinations produce high motor amperage draw due to friction, causing the deck or motor to wear out faster than the treadmill belt. Replacement of such decks often involves significant disassembly of the treadmill to remove a worn deck from the treadmill frame and install a deck with a fresh wear surface. Due to the cost and service needs of replacing these bulky and heavy monolithic decks, many users consider the treadmill life spent when the deck wears out. 
         [0005]    Most commercial treadmills use thick decks (e.g., one inch thick) weighing approximately 4.5 lbs per sq. feet or over 40 pounds total. Such decks are typically wider than the treadmill belt and are mounted to frame rails with trim strips covering the mounting bolts along the longitudinal edges of the treadmill deck. 
         [0006]    Accordingly, improvements are sought in the production, wear and replacement of treadmill decks. 
       SUMMARY 
       [0007]    One aspect of the invention features a thin laminate including a rigid or semi-rigid core having a first broad top face and a second broad bottom face and a phenolic impregnated fibrous layer laminated to each of the first and second broad faces of the core. 
         [0008]    In some embodiments, the phenolic impregnated fibrous layer includes kraft paper. 
         [0009]    In some cases, the laminate surface has a smooth finish to provide a low friction wear surface. 
         [0010]    In some cases, the laminate is less than about 5/16 inch. In some cases, the laminate is less than about ¼ inch thick. In some cases, the laminate is less than about 3/16 inch thick. 
         [0011]    In some cases, the laminate includes a phenolic impregnated fibrous layer on both faces of the laminate. 
         [0012]    In some cases, the fibrous layer includes multiple sheets of kraft paper. In other cases, the fibrous layer includes a single heavier weight sheet of kraft paper. 
         [0013]    One aspect of the invention features a treadmill deck assembly including a rigid deck support having a broad top surface configured to extend at least substantially the width of a treadmill belt. A rigid or semi-rigid deck insert is disposed on the top surface of the deck support and includes a fibrous deck insert core of less than about 5/16 inch, having a first broad top face and a second broad bottom face and a phenolic impregnated fibrous layer laminated to each of the first broad top face and the second broad bottom face of the deck insert core to provide a reduced friction wear surface for the treadmill belt. 
         [0014]    In some embodiments, the deck insert core includes isocyanate resin and has a moisture content of less than about four percent prior to lamination with the phenolic impregnated paper. In some embodiments, the deck insert core has a moisture content of less than about four percent after lamination with the phenolic impregnated paper. 
         [0015]    In some embodiments, the multiple phenolic impregnated fibrous layers are provided on both faces of the deck insert core. In some embodiments, the deck insert is configured to be mated on either face with the deck support such that the deck insert is reversible to provide a fresh wear surface for the treadmill belt. 
         [0016]    Another aspect of the invention features a treadmill deck insert including a rigid or semi-rigid core of medium density fibers bonded with isocyanate resin of less than about 5/16 inch thickness, having a first broad face and a second broad face and a moisture content of less than about four percent. In some content the moisture content is between about three and four percent. In other cases, the moisture content is less than about three percent. A phenolic impregnated fibrous layer is laminated to both broad faces of the core and configured as a wear surface for use with a belt of a treadmill. 
         [0017]    In some embodiments, the phenolic impregnated fibrous layer includes kraft paper. The kraft paper has a basis weight of between about 40-80 grams per square meter and is saturated at between about 55-75% with a fast cure phenolic resin. In some cases, the kraft paper has a basis weight of about 47 grams per square meter and is saturated at 65.5% with a fast cure phenolic resin. 
         [0018]    In some cases, a second phenolic impregnated fibrous layer is laminated to at least one of the broad faces of the core. In some cases, multiple layers of phenolic impregnated fibrous material are disposed on the first and second broad faces of the substrate. 
         [0019]    In some embodiments, the insert has an internal bond strength of between about 180-250 psi. In some embodiments, the insert has an internal bond strength of at least about 200 psi. In some embodiments, the insert has an internal bond strength of at least about 220 psi. 
         [0020]    Some embodiments of the invention include a deck insert with one or more of the following features: an internal bond strength of between about 180-250 psi, an internal bond strength of about 180 psi, a thickness of less than about 5/16, a thickness of less than about ¼ inch, a moisture content of less than about 4%, a moisture content of about 3%; and a surface finish of between about 6-20 Ra. 
         [0021]    Another aspect of the invention features a treadmill including a frame having first and second opposed ends, a first powered roller disposed at the first frame end, and a second roller disposed at the second frame end. A treadmill deck having an upper broad surface and a lower broad surface and supported on the frame between the first and second rollers and continuous belt is trained about the first and second rollers over the upper broad surface of the deck. A deck insert is disposed on the upper broad surface of the deck adjacent the belt, the insert including a phenolic resin impregnated kraft paper layer laminated to first and second broad surface of a medium density fiber isocyanate resin bonded core having a moisture content of less than about 4% and a thickness of less than about 5/16 inch. 
         [0022]    In some embodiments, the treadmill further includes a second resin impregnated kraft paper layer laminated to one of the first and second broad surface of the core to provide low friction wear surface. 
         [0023]    In some embodiments, the deck insert is configured to be readily removable, reversible and reinstallable between the belt and deck support without substantial disassembly of the treadmill. 
         [0024]    In some embodiments, the insert is less than about ¼ inch thick. In other cases, the deck is between about ¼ inch thick and 5/16 inch thick. 
         [0025]    Another aspect of the invention features a method of manufacturing a treadmill deck insert including providing a rigid or semi-rigid fibrous substrate having a first broad surface and a second broad surface and a moisture content of less than about four percent, saturating kraft paper with basis weight of between about 40-80 grams per square meter to between about 55-75% with phenolic resin, disposing a first layer of the phenolic saturated kraft paper on the first broad surface of the substrate, disposing a second layer of the phenolic saturated kraft paper on the second broad surface of the substrate, and laminating the paper layers to the substrate at high temperature and pressure to form a deck insert having a low friction wear surface on opposite broad faces. 
         [0026]    In some applications, the method includes disposing an additional layer of phenolic saturated kraft paper on one of the first and second broad surfaces of the substrate. In some applications, the method includes disposing additional layers of phenolic saturated kraft paper on both surfaces. 
         [0027]    In some applications, the laminating is performed at about 200 bars pressure and about 170 C temperature for about 60 seconds. 
         [0028]    In some applications, the method includes forming countersunk holes along the periphery of the two opposite faces of the insert. 
         [0029]    In some applications, the laminated deck insert is less than about 5/16 inch thick. 
         [0030]    In some applications, the laminated deck insert is about ¼ inch thick, has an internal bond strength of about 200 psi and a surface finish of between about 6-20 Ra micro inches. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0031]      FIG. 1  is a perspective view of one treadmill embodiment. 
           [0032]      FIG. 2  is partial perspective view of a deck assembly embodiment. 
           [0033]      FIG. 3  is a cross-sectional view of the treadmill of  FIG. 1  taken along line  3 - 3 . 
           [0034]      FIG. 4  is a flow chart showing a method of making a treadmill deck insert. 
       
    
    
       [0035]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0036]    With reference to  FIG. 1 , one embodiment of a treadmill  10  includes a rigid frame  12  supporting a treadmill deck assembly  14 . First and second rollers  16  are supported by frame  12  at either end of deck assembly  14 . Generally, one of the rollers  16  is powered by a variable speed motor (not shown). An endless belt  18  is trained and tensioned about the rollers over deck assembly  14 . 
         [0037]    Deck assembly  14  is wider than belt  18 , or at least substantially as wide as belt  18 , and is supported and fastened on frame  12 . Trim panels  19  cover the fasteners and portion of deck assembly that extends beyond the width of belt  18  and can provide a resting footing location for the treadmill user. 
         [0038]    With reference to  FIGS. 2-3 , treadmill deck assembly  14  includes a deck support  20  beneath a deck insert  26  that serves as a low friction wear surface  28  for belt  18 . Deck support  20  includes a first top surface  22  on a top side. Deck support  20  can be plywood, medium density fiberboard (MDF), metal, plastic or other material suitable to support the weight and impact of a runner&#39;s footsteps. 
         [0039]    Treadmill deck insert  26  is positioned on the first broad surface of deck support  20  with wear surface  28  adjacent belt  18 . Insert  26  comprises an insert core  30  and a resin impregnated paper layer  32  laminated across a first broad surface  34  on a top side of core  30  and a second broad surface on a bottom side of core  30 . 
         [0040]    Lamination of core  30  and paper layers  32  is performed in a high temperature, high pressure laminating press. It was determined through experimentation that standard MDF and plywood materials, which typically have a moisture content of 5-6% or higher, were not suitable for use in thin laminates with phenolic impregnated paper due to delamination and dimensional stability concerns. 
         [0041]    It was determined through significant continued experimentation that use of an isocyanate resin MDF material with a reduced moisture content of about 3-4% or less resulted in durable lamination of a phenolic impregnated paper layer  32  to a fiberboard core  30  with good wear surface characteristics. This was particularly significant in enabling lamination with very thin MDF cores  30  of about ¼ inch or less. 
         [0042]    Another embodiment of deck insert  26  comprises multiple phenolic saturated kraft paper layers  32  applied to both sides of core  30 . Paper layer  32  has a basis weight of about 40-80 grams per square meter and is saturated or impregnated to 55-75% with a fast cure phenolic resin. One particular embodiment includes kraft paper having basis weight of about 47 grams per square meter that is saturated to about 65.5% with phenolic resin. 
         [0043]    In some cases, core  30  is less than about 5/16 inch thick, or less than about ¼ inch thick, and has a moisture content of less than about 4% or of about 3%. 
         [0044]    In some embodiments, a second resin impregnated paper layer is provided on a second broad surface on a bottom side of core  30  such that insert  26  is reversible to provide a fresh wear surface  28 . In some embodiments, deck insert  26  can include more than one sheet of impregnated paper  32  on one or more broad surfaces of insert  26 . In some cases, a heavier basis weight single layer of kraft paper is used. 
         [0045]    With reference to  FIG. 4 , a method of making deck insert  20  includes providing an isocyanate resin MDF deck insert core  30  having a moisture content of less than about 4%. ( 40 ) Low moisture content of the core is preferably preserved prior to lamination as moisture content greater than about 3-4% causes paper layer  32  to delaminate from core  30  in the press. For example, core  30  can be enclosed in a sealed packaging to exclude ambient moisture from increasing the effective moisture content of core  30 . The core is then removed from the scaled packaging just prior to lamination. 
         [0046]    Deck core  30  is formed from an MDF panel, which is refined wood fibers and isocyanate resin formed into a matte and press cured into uniform panels at high pressure (e.g., 900 psi) and high temperature (e.g., 365 degree Fahrenheit). The moisture of the wood fines and curing parameters arc controlled to provide a finished MDF panel having a moisture content of less than about 4%, and preferably about 3%. 
         [0047]    One suitable MDF core  30  has the following properties: a moisture content between 3-4%, a fiber density of about 50-52 lbs per cubic foot, a resin percentage of about 3%, a core thickness of about ¼ inch with an internal bond of 180-250 psi. For even thinner deck embodiments, fiber density of about 55 lbs per cubic foot and about 4% resin can be used to obtain relatively high internal bond values (about 250 psi) to prevent core and face delamination. 
         [0048]    The method includes sizing MDF deck inset core  30  to fit in a laminating press. ( 42 ) The laminating press can accommodate sufficient material for one or more finished deck inserts  26  at a time. ( 42 ) 
         [0049]    The method includes saturating kraft paper with phenolic resin to form phenolic impregnated paper layer  32 . ( 44 ). The kraft paper has a basis weight of between about 40-80 grams per square meter and is saturated at 55-75% with a fast cure phenolic resin. In a particular embodiment, the kraft paper has a basis weight of 47 grams per square meter and is saturated to 65.5% by weight with a fast cure phenolic resin. A suitable phenolic saturated kraft paper is available from Arclin Surfaces of Tacoma, Wash., including kraft paper available from Nordic Paper of Sweden and phenolic resin number R3485 or R3486. 
         [0050]    One ore more layers of phenolic impregnated paper  32  are then provided on both faces of MDF core  30  to form a prelaminate lay-up. ( 46 ) The paper and core lay-up is placed in a high speed laminating press and laminated at high temperature and pressure. ( 48 ). The phenolic saturated kraft paper layers  32  and isocyanate MDF core  30  are thus thermofused to produce a laminate with an internal bond value of about 200 psi. This is a significant increase over the internal bond values of about 140 psi for existing urea formaldehyde MDF panels or thicker and higher moisture content MDF panels. By closely controlling the moisture content in the precursor isocyanate MDF panels, a suitable thin deck insert  26  was achieved using a press cycle time of 60 seconds, at 200 bars pressure and 338 degrees Fahrenheit. The laminated core and paper panel is then finish cut into individual insert decks  26 . ( 50 ). 
         [0051]    The laminating press includes stainless hard chromed surfaced plates with a 6-20 Ra micro inch finish to impart a smooth finish to wear surface  28  of the exposed faces of deck insert  26 . This has been determined to be sufficiently smooth to enable a polyester treadmill belt to glide over wear surface  28  under the intense repeated pressure during footsteps of a runner on deck assembly  14 . The phenolic resin on the paper surface provides a suitable taber abrasive value resulting in a relatively long useful life comparable to the thicker phenolic coated panels currently used in commercial treadmills. The thin deck insert  26  provides a low friction surface with reduced amperage draw. A paraffin, carnauba or polyolefin based wax can also be added to the wear surface of deck insert  26  or the underside of belt  18  for lubrication purposes. 
         [0052]    The thin deck insert  26  is mated during treadmill assembly to a sub support deck  20  made of plywood, particleboard, MDF, plastic, steel or other ferrous or non ferrous materials. The thin insert deck  26  need not be as wide as the underlying support deck  20 . This provides a significant cost of manufacturing advantage over existing monolithic phenolic decks. Furthermore, in contrast to the bulky, heavy prior art decks, a thin, e.g. ¼ inch, insert deck  26  weighs a mere one pound per square foot. This provides significant savings in handling, shipping and installation of replacement deck inserts. Some thin insert embodiments are reversible to provide two useful wear surfaces  28 . 
         [0053]    Insert deck  26  can be mechanically fastened along its longitudinal periphery with countersunk fasteners (e.g., screws) to an underlying deck support  20 . In alternative embodiments, deck support  30  and deck insert  20  are formed with complementary interlocking features. For example, deck support  20  can include a recess to retain deck insert  26 . Other fastening means such as touch fasteners, rivets, adhesives and the like can also be used. Deck support  20  is fastened to frame  12  of treadmill  10  with bolts or the like, which are then covered by trim panels  19 . Trim panels  19  can also cover the countersunk fastenings securing thin deck  26  to deck support  20 . Alternatively, the countersunk fastenings can be located under the periphery of belt  18 . 
         [0054]    Accordingly, deck insert  26  is readily reversible or interchangeable simply by removal of trim panels  19  and deck insert fasteners to enable removal and reinstallation of the insert between belt  18  and deck support  20 . Thus, in many cases, belt  18  need not be loosened nor deck support  20  removed to provide a fresh wear surface  28  under belt  18 . This provides a significant savings of time and service expense in maintaining treadmill  10 . 
         [0055]    Accordingly, various embodiments provide advantages including at least simplicity, reduced production costs, reduced shipping cost and reduced replacement labor and costs. 
         [0056]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, other fabrics or nonwoven materials may be used in place of kraft paper and non-wooden fibers may be used to form the insert core. Accordingly, other embodiments are within the scope of the following claims.