Abstract:
The disclosed embodiments herein are generally directed toward force-balancing mechanisms for weighted members and/or loads. According to one embodiment, the force-balancing mechanism includes at least one gear rack, at least one spring assembly comprising a spring member operatively connected to the at least one gear rack, a pinion gear intermeshed with the at least one gear rack; and a variable radius cam. Rotation of the cam causes the pinion gear to rotate to thereby in turn linearly drive the at least one gear rack and accumulate spring force of the spring member. The spring member may be a compression or a tension spring. Preferably, the spring member is a compression spring.

Description:
FIELD 
     The embodiments disclosed herein relate generally to force-balancing mechanisms for weighted members and/or loads. In especially preferred embodiments, force-balancing mechanisms are provided that are usefully employed for the force-assisted lifting/lowering of aircraft stairs. 
     BACKGROUND 
     Integrated aircraft stairs to allow passengers to board and disembark when the aircraft fuselage door is opened are colloquially known as “airstairs”. Aircraft which include airstairs can thus provide service to many less populated airport environments since a fixed-based gantry platform to allow passengers to board and disembark is not necessarily required. For these reasons, many regional transport and general aviation aircraft are equipped with airstairs as the primary means to allow boarding and disembarking of passenger and aircraft crew members. 
     In general, most conventional force-balancing mechanisms for airstairs use space-saving torsional bars to accumulate weight energy and power sufficient to provide lift assistance. In this regard, such conventional airstairs will typically employ an actuator/gearbox, which are interconnected by a torsion bar. When the torsion bars are twisted, a large load is accumulated at the ends of the torsion bars which over time results in fatigue failure. When failure occurs, the airstairs may become inoperable resulting in aircraft downtime to allow for repair. As a result, conventional force-balancing mechanisms for airstairs are somewhat problematic due to this continued potential maintenance issue. 
     What has been needed therefore are space-saving force-balancing mechanisms for loads that are more durable, especially force-balancing mechanisms for loads associated with airstairs for aircraft. It is towards fulfilling such needs for force-balancing mechanisms that the embodiments as disclosed herein are provided. 
     SUMMARY 
     The disclosed embodiments herein are generally directed toward force-balancing mechanisms for weighted members and/or loads. According to one embodiment, the force-balancing mechanism comprises at least one gear rack, at least one spring assembly comprising a spring member operatively connected to the at least one gear rack, a pinion gear intermeshed with the at least one gear rack; and a variable radius cam. Rotation of the cam causes the pinion gear to rotate to thereby in turn linearly drive the at least one gear rack and accumulate spring force of the spring member. The spring member may be a compression or a tension spring. Preferably, the spring member is a compression spring. 
     According to some embodiments the force-balancing mechanism may include a pair of gear racks each intermeshed with the pinion gear, and a pair of spring assemblies. The pair of spring assemblies may be arranged parallel to one another or may be arranged opposite to one another. 
     The spring assembly may include spaced-apart fixed and moveable end supports between which the spring member is positioned. According to some embodiments, the fixed end support is positioned proximal to the pinion gear and wherein the moveable end support is positioned distal to the pinion gear. A connection rod may be provided to connect the moveable end support to an end of the at least one gear rack. According to other embodiments, the fixed end support is positioned distal to the pinion gear and wherein the moveable end support is positioned proximal to the pinion gear. In such embodiments, the moveable end support may be connected directly to an end of the at least one gear rack. 
     A flexible actuator cable having one end fixed to a terminal lobe of the cam, and an opposite end for fixed connection to supporting structure (e.g., to aircraft structure supporting an airstair). 
     The force-balancing mechanism may be usefully employed to force-balance virtually any moveable weighted member or load. In preferred embodiments, the weighted member is an aircraft airstair. Thus, in accordance with other embodiments, the force-balancing mechanism is provided in an aircraft airstair. 
     These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof. 
    
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
       The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative embodiments in conjunction with the drawings of which: 
         FIGS. 1A and 1B  are exterior perspective views of a forward aircraft fuselage showing the associated airstair in stowed and deployed positions, respectively; 
         FIG. 2  is an enlarged detail view of an airstair in a stowed position; 
         FIG. 3  is an enlarged detail view of an airstair in a deployed position; 
         FIGS. 4A and 4B  are enlarged detailed side elevational views of an embodiment of a force-balancing mechanism having a dual parallel spring assembly and depicted in force unloaded (stowed) and loaded (deployed) conditions, respectively; 
         FIG. 5  is an enlarged detailed side elevational view of another embodiment of a force-balancing mechanism having a dual opposed spring assembly and depicted in a force unloaded (stowed) condition; 
         FIG. 6  is an enlarged detailed side elevational view of a variant of the force-balancing mechanism shown in  FIG. 5 ; 
         FIG. 7  is an enlarged detailed side elevational view of an embodiment of a force-balancing mechanism employed in the airstair having a single spring assembly and depicted in force unloaded (stowed) condition; and 
         FIG. 8  is an enlarged detailed side elevational view of a variant of the force-balancing mechanism shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Accompanying  FIGS. 1A and 1B  are exterior perspective views of a forward section of an aircraft fuselage  10  equipped with a fuselage opening  12  and a conventional door  14  to close the opening  12 . A foldable airstair  18  is provided in the opening  12  and is equipped with a force-balancing mechanism  20  according to one embodiment of the present invention. 
     Accompanying  FIGS. 2-3  depict the airstair  18  in greater detail in stowed and deployed conditions, respectively. In this regard, it will be observed that the airstair is provided with respective upper and lower (relative to airstair deployment) airstair sections  18 - 1 ,  18 - 2 , respectively, connected together at hinge point  22  to allow relative hinged articulation therebetween. An upper end of the upper section  18 - 1  includes an attachment bracket  24  which is connected to a fixed base  26  for pivotal movements about a generally horizontal pivot axis. The base  26  is rigidly connected to supporting structure  10 - 1  associated with the aircraft fuselage  10 . A ground-engaging section  18 - 3  is pivotally hinged to the lower free end of the lower airstair section  18 - 2  at hinge connection  25  so as to be pivotal between a stowed condition (see  FIG. 2 ) and a deployed condition (see  FIG. 3 ). Wheels  27  are provided with the section  18 - 3  so as to engage the ground G when the airstair  18  is fully deployed. The airstair sections  18 - 1 ,  18 - 2  and  18 - 3  are provided with stair treads  18 - 4  to allow passengers and crew members to board and disembark when the airstair  18  is in a deployed condition. 
     The force-balancing mechanism  20  employed in the airstair  18  is depicted in greater detail in accompanying  FIGS. 4A and 4B . In this regard, the force-balancing mechanism  20  is depicted by  FIGS. 4A and 4B  in a common orientation so that the structural positioning of the various components in force-unloaded and force-loaded conditions corresponding to the airstair stowed and deployed conditions, respectively, can be readily discerned. Thus, it will be understood that when in the force-unloaded condition depicted by  FIG. 4A , the force-balancing mechanism  20  will be in a position with the airstair  18  as depicted by  FIG. 2 , whereas when in the force-loaded condition depicted by  FIG. 4B , the force-balancing mechanism will be in a position with the airstair  18  as depicted in  FIG. 3 . 
     The embodiment of the force-balancing mechanism  20  depicted in  FIGS. 4A and 4B  is generally comprised of a pair of parallel helical compression spring assemblies  30 ,  32  which include helical compression springs  30 - 1 ,  32 - 1  coupled operatively to rack gears  30 - 2 ,  32 - 2 , respectively. More specifically, each of the springs  30 - 1 ,  32 - 1  is mounted between fixed and moveable end supports  30 - 3   a,    32 - 3   a  and  30 - 3   b ,  32 - 3   b,  respectively. The fixed end supports  30 - 3   a,    32 - 3   a  are thus immovably fixed to structure associated with the upper airstair section  18 - 1  (a portion of which is shown in  FIGS. 4A and 4B ), while the movable end supports  30 - 3   b,    32 - 3   b  are fixed to and moveable with the rack gears  30 - 2 ,  32 - 2 , respectively. It will be observed in this regard that the moveable end support  30 - 3   b  is connected directly to an end of the rack gear  30 - 2  whereas the moveable end support  32 - 3   b  is connected to the rack gear  32 - 2  by way of an elongate connection rod  33 . 
     The rack gears  30 - 2 ,  32 - 2  are meshed with a pinion gear  34  which is mounted to the pinion axle  36  for rotational movement about the axis thereof. A continually variable radius (“nautilus-type”) cam  38  is also connected to the pinion axle  36  so as to be rotatable as a unit with the pinion gear  34  about the axis of the pinion axle  36  (i.e. as shown by arrow A 1  in  FIG. 2 ). The profile of the nautilus-type cam  38  is such that a different radius is presented at successive different degrees of rotation thereof to provide moment arms of varying lengths as the cam  38  is rotated about the axis of the axle  36 . 
     As is perhaps best shown in  FIGS. 2 and 3 , a flexible actuator cable  40  is provided with one end pivotally connected to the fixed base  26  and an opposite end connected to the terminal lobe  38 - 1  of cam  38 . Thus, as the upper airstair section  18 - 1  pivots from its stowed position to a deployed condition, the actuator cable  40  will cause the cam  38 , and hence the pinion gear  36 , to rotate in the direction of arrow A 1 . Rotation of the pinion gear  36  will in turn cause the rack gears  30 - 2 ,  32 - 2  to move linearly in the direction of arrows A 2  and A 3  as shown in  FIG. 4A  thereby compressing each of the compression springs  30 - 1  and  32 - 1 , respectively. Thus, as the upper airstair section  18 - 1  pivots from its stowed position to a deployed condition, the force-balance mechanism  20  will translate from its force-unloaded condition as shown in  FIG. 4A  (i.e., whereby the compression springs  30 - 1 ,  32 - 1  have minimal if any stored compression force) to a force-loaded condition as shown in  FIG. 4B  (i.e., whereby the compression springs  30 - 1 ,  32 - 1  have substantial or maximum stored compression force). The loaded compression force that is accumulated when the upper airstair section  18 - 1  is in its deployed condition may thereby be used to provide force-assisted movement back to the stowed condition from the deployed condition thereof (i.e., when the cam  40  is rotated in a direction opposite to arrow A 1 ). 
     Accompanying  FIGS. 5-9  depict other embodiments of force-balancing mechanisms according to the invention. In this regard, although not depicted in  FIGS. 5-9 , the embodiments shown will include a continually variable radius (“nautilus-type”) cam of the type shown, for example by reference numeral  38  in  FIGS. 4A and 4B  which is connected to the pinion axle  36  so as to be rotatable as a unit with the pinion gear  34  about the axis of the pinion axle  36 . Thus, such a cam  38  will similarly be connected to a fixed base structure  26  via an actuator cable  40  or like mechanisms as described previously. 
     The force-balancing mechanism  50  depicted by  FIG. 5  is a variant of the dual spring assembly mechanism  20  described above. Specifically, it will be observed that the mechanism  48 , like the mechanism  20 , has dual compression spring assemblies  50 ,  52 . However, unlike the mechanism  20 , the mechanism  48  is arranged so that the compression spring assemblies  50 ,  52  are opposite to one another. Thus, the spring assemblies  52  include helical compression springs  50 - 1 ,  52 - 1  coupled operatively to rack gears  50 - 2 ,  52 - 2 , respectively. More specifically, each of the springs  50 - 1 ,  52 - 1  is mounted between fixed and moveable end supports  50 - 3   a,    52 - 3   a  and  50 - 3   b,    52 - 3   b,  respectively. The fixed end supports  50 - 3   a,    52 - 3   a  are thus immovably fixed to structure associated with the upper airstair section  18 - 1  (a portion of which is shown in  FIG. 5 ) at a position proximal to the pinion gear  36 , while the movable end supports  50 - 3   b,    52 - 3   b  are fixed to and moveable with the rack gears  50 - 2 ,  52 - 2 , respectively, at a position distal to the pinion gear  36 . It will be observed in this regard that the moveable end supports  50 - 3   b ,  52 - 3   b  are connected to an end of the rack gears  50 - 2 ,  52 - 2  by way of an elongate connection rod  50 - 4 ,  52 - 4 , respectively. 
     Rotation of the pinion gear  38  in the manner described above during pivotal movement of the upper airstair section  18 - 1  into the deployed condition thereof will thus linearly drive each of the rack gears  50 - 2  and  52 - 2  in the direction of arrows A 2  and A 3  thereby causing the springs  50 - 1 ,  52 - 1  to be compressed. As such, the force-balancing mechanism  48  is caused to assume a force-loaded condition so that the accumulated spring force is available to assist when the upper airstair section is moved back into its stowed condition. 
       FIG. 6  depicts a variant of the embodiment shown in  FIG. 5  whereby similar structural elements are noted by a prime (′) symbol. As shown, the embodiment of  FIG. 6  includes fixed position end supports  50 - 3   a ′,  52 - 3   a ′ which are distal to the pinion gear  38  and moveable end supports  50 - 3   b ′,  52 - 3   b ′ that are proximal to the pinion gear  38  (i.e., generally opposite to the embodiment shown by  FIG. 5 ). The moveable end supports  50 - 3   b ′,  52 - 3   b ′ are moreover fixed directly to an end of the rack gears  50 - 2 ′,  52 - 2 ′ (thereby avoiding the need for the connection rods  50 - 4 ,  52 - 4  of the embodiment shown by  FIG. 5 ). In a similar manner, however, during pivotal movement of the upper airstair section  18 - 1  into the deployed condition thereof, each of the rack gears  50 - 2 ′ and  52 - 2 ′ will be driven linearly in the direction of arrows A 2  and A 3  thereby causing the springs  50 - 1 ′,  52 - 1 ′ to be compressed. As such, the force-balancing mechanism  48 ′ is caused to assume a force-loaded condition so that the accumulated spring force is available to assist when the upper airstair section is moved back into its stowed condition. 
     Single compression spring embodiments of the force-balancing mechanisms are shown in  FIGS. 7 and 8  and may be used in those instances where lighter duty requirements are needed (i.e., thereby avoiding the weight penalty of a second compression spring and its associated components while yet still providing for sufficient force assistance). More specifically, the force balancing mechanism  60  as shown in  FIG. 7  includes a single compression spring  60 - 1  mounted between a fixed end support  62  connected to the upper airstair section  18 - 1  at a position proximal to the pinion gear  36 , and a moveable end support  64  positioned distal to the pinion gear  36 . The moveable end support  64  is connected to the gear rack  66  by way of a connection rod  65 . Rotation of the pinion gear  36  during movement of the upper airstair section  18 - 1  from its stowed condition to the deployed condition will therefore effect force-loading in a similar manner to that described above in connection with spring assembly  52  of  FIG. 5 . 
     The force balancing mechanism  60 ′ as shown in  FIG. 8  includes a single compression spring  60 - 1 ′ mounted between a fixed end support  62 ′ connected to the upper airstair section  18 - 1  at a position distal to the pinion gear  36 , and a moveable end support  64 ′ positioned proximal to the pinion gear  36 . The moveable end support  64 ′ is directly connected to an end of the gear rack  66 ′ (thereby avoiding the need of the connection rod  65  as shown in  FIG. 7 ). Rotation of the pinion gear  36  during movement of the upper airstair section  18 - 1  from its stowed condition to the deployed condition will therefore effect force-loading in a similar manner to that described above in connection with spring assembly  52 ′ of  FIG. 6 . 
     It will be appreciated that the force-balancing mechanisms in accordance with the various embodiments have been described in connection with an especially preferred end-use application, that is as a force-balancing mechanism for aircraft airstairs. However, the force-balancing mechanisms as described herein could also be suitable used for virtually any purpose where mechanical lift and/or deployment force-assistance is desired for virtually any weighted member, for example, doors, hatches, gantry platforms, overhead stairs and the like. Thus, the use of the force-balancing mechanisms for assisting in the stowage/deployment of airstairs as described herein is understood to be a presently preferred, but non-limiting, embodiment thereof. 
     Furthermore, it is currently envisioned that compression springs are preferred. However, those skilled in this art could envision modifications which employ tension springs in which case such modifications are entirely within the scope of the embodiments as described herein. 
     Therefore, while the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.