Abstract:
A polycarbonate window system having an integrated ROPS that reduces the thickness of cab posts of machine such that the operator&#39;s visibility is increased. The polycarbonate window system also facilitates secure retention of the polycarbonate window without requiring holes to be formed near the periphery of the polycarbonate window, thereby increasing the structural integrity of the polycarbonate window.

Description:
TECHNICAL FIELD 
     This disclosure relates generally to window frame systems, and more specifically, to window frame systems for polycarbonate windows having integrated roll over protection. 
     BACKGROUND 
     Several mobile machines, especially those used in forestry applications such as, e.g., forwarders, skidders, or feller bunchers, have a cab structure to protect the operator that includes a roll over protection structure (ROPS). For example, Frett et al. disclose a work vehicle including a typical operator cab frame and a roll-over protective structure mounted to the frame (published U.S. Patent Application No. 2008/0048426). Also, International ROPS Standards, such as ISO3471, SAEJ1040, AS2294.2, require that the operator cab withstand given lateral, vertical and longitudinal forces, as well as absorb a minimum lateral energy. In a machine roll over, the energy absorbing criteria assists in slowing down the lateral rotation of the machine. For conventional construction machinery ROPS, generally a rectangular tubular frame may absorb lateral energy by bending at the corners, in the manner of a parallelogram, without intruding into a defined operator space or coming up against the machine chassis. 
     Further, mobile machines that are used in a setting where they are often in physical contact with the environment, such as forestry settings, utilize polycarbonate windows to prevent damage to the windows and the operator. To accommodate both the ROPS and the use of polycarbonate windows, many machines have thick corner posts that may obstruct the operator&#39;s view and a polycarbonate window that is bolted into a frame through the window&#39;s periphery. 
     In the past, a machine&#39;s ROPS was the primary focus of the design, and thick, wide posts were incorporated in the ROPS. However, as different materials and different post substructures have developed, such as multi-walled tubes or waved shaped supporting post substructures, the material required to be used in a suitable ROPS post has decreased. Such a transition has also been motivated, in part, by the desire to increase operator visibility. 
     Another way that operator visibility was hampered in the past was the presence of a distinct ROPS post and a window frame. The window frame was commonly joined to the ROPS post or frame, then the windows were inserted to the frame and fastened in place, such as with a bolt through the window&#39;s periphery and into the frame when an outer plate was used to effectively sandwich the glass between the outer plate and the window frame. Overall, this additional structure further decreased operator visibility. 
     The present invention is directed to overcome one or more of the problems as set forth above. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present disclosure is directed to a window framing system comprising a continuous polycarbonate window having a thickness, t; a post system having a main post body and a post protrusion that extends from the main post body a distance of at least about t; and a retainer fixedly attached to the post system. It is also directed to a cab of a mobile machine and a forestry forwarder having such a window framing system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of an operator cab of a forestry forwarder according to the immediate disclosure. 
         FIG. 2  is a cross-sectional view of a post system of the operator cab. 
         FIG. 3  is an exploded view of the post system of the operator cab. 
         FIG. 4  is a cross-sectional view of the post system with a retainer ledge. 
         FIG. 5  is a schematic representation of a post system having discontinuous post protrusions. 
         FIG. 6  is an exploded view of the post system of the operator cab having a discontinuous seal. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a forestry forwarder  110  will be referenced herein for exemplary purposes only, while the scope of the invention is more accurately reflected by the accompanying claims and applies to other mobile machines. Forestry forwarder  110  comprises an operator cab  112 , the structure of which comprises post system  114 , windows  116 , and a roof  118 , as shown in  FIG. 2 . The roof  118  and post system  114  are also components of the machine&#39;s ROPS. 
       FIG. 2  shows a cross-section of post system  114  while  FIG. 3  shows an exploded view of the same. Post system  114  comprises a main post body  120  that is of appropriate dimensions to satisfy any ROPS requirements and maximize operator viewing area. For example, regardless of whether main post body  120  is triangular, tetrahedral, octagonal, circular, or some other geometric shape, the distance between the furthest two points of main post body  120  in cross-section is between about 2 inches and about 12 inches, such as between about 4 inches and about 9 inches. For example, when main post body  120  is tetrahedral, main post body  120  is between about 2 inches and about 5 inches wide and between about 2 inches and about 5 inches thick, such as between about 3 inches and about 4.5 inches wide and between about 3 inches and about 4.5 inches thick. 
     Post system  114  is designed such that it includes a post protrusion  310 , which is a feature that protrudes to align with the edge of windows  116  and extends from main post body  120  a distance of at least the thickness of window  116 , such as between about 0.25 inches and about 1.0 inches. Post protrusion  310  may be continuous, such that post protrusion  310  is a feature present around all of window  116 . In other embodiments, post protrusion  310  is discontinuous, such that the protrusions are strategically located around window  116 , as shown in  FIG. 5 . 
     As shown in  FIG. 2 , post protrusion  310  may take the shape of a smaller, partial version of main post body  120 . Post protrusion  310  effectively acts as a spacer to stabilize and position the windows  116  in the correct orientation. Post protrusion  310  may be configured to partially support a retainer  320 , which extends over the windows  116  to hold them in place when retainer  320  is secured to post system  114 , i.e., to main post body  120  or to post protrusion  310 . 
     In an alternative embodiment, post system  114  comprises post protrusion  310  and a retainer ledge  410  that is designed to partially support retainer  320 , as shown in  FIG. 4 . Retainer ledge  410  extends beyond post protrusion  310  by a distance approximately equal to the thickness of retainer  320 , such as by between about 0.1 inches and about 0.5 inches. For example, retainer ledge  410  typically extends beyond post protrusion  310  by between about 0.15 inches and about 0.25 inches. In this way, retainer  320  is oriented such that its outer surface is flush with the outer surface of post protrusion  310 . 
     Moreover, post protrusion  310  may be configured to extend continuously around main post body  120 , as shown in  FIG. 3 , or post protrusion  310  may be arranged at particular intervals around main post body  120 , as shown in  FIG. 5 . 
     Windows  116  are made of a polycarbonate polymer material and of an appropriate thickness, t, to withstand encounters with objects from the environment, such as tree branches or limbs. For example, windows  116  may be between about 0.25 inches and about 1.0 inches thick, such as between about 0.4 inches and about 0.7 inches thick. In one example, windows  116  are about 0.5 inches thick. The thickness of window  116  is substantially similar over the length and width of window  116 . Furthermore, windows  116  may comprise a polarizing film to diminish ultraviolet (UV) radiation impact on the operator, such as reducing UV glare. Polycarbonate windows  116  are also continuous material, i.e., there are no features such as bolt holes formed near the periphery of window  116 . 
     Seals  330  may be included to firmly hold the window  116  stationary. Seals  330  can be arranged in any desired orientation on main post body  120  and/or retainer  320  to achieve such a stabilizing effect. Seals  330  may be attached to main post body  120  and/or retainer  320  using any suitable means, such as adhesives or fasteners. Seals  330  comprises an elastic or foamed polymeric material that can support window  116  in its intended position without compromising the integrity of window  116 . The seals may be continuous, such that the entire periphery of window  116  is sealed, or it may be discontinuous, such that gaps in the seal are present, as seen in  FIG. 6 . 
     INDUSTRIAL APPLICABILITY 
     The disclosed cab achieves two important improvements for operator use of the machine. First, post system  114  are smaller than previous posts and window framing systems because the framing system is integrated into posts  114 . By utilizing such an arrangement, the operator&#39;s visibility is dramatically increased. Moreover, by using less raw materials to form post system  114  than in previous examples, a cost advantage may be realized. However, this advantage does not compromise the ROPS requirements by still maintaining appropriate minimum material and dimensional characteristics for post system  114 . 
     Second, designing post system  114  to have retainer  320 , which is designed to be joined or secured to post system  114 , and seals  330  allows window  116  to be securely held in position without having holes formed or cut into the periphery of window  116  as in previous designs. Such holes would be designed into prior art windows so bolts or other fasteners may pass through the window before encountering post system  114 . The lack of such holes in the immediately disclosed polycarbonate window is important, in part, because polycarbonate window manufacturers propose that sheets of polycarbonate should be retained in their state as a continuous object without holes or other features cut out of the polycarbonate. Such features can act as stress points and compromise the integrity of the polycarbonate object, i.e., window  116 . Therefore, the disclosed window framing system allows the manufacture of cabs that afford increased visibility for operators while simultaneously improving the integrity of polycarbonate windows  116 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope or spirit of the invention. Additionally, other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only.