Abstract:
A two-rail rear ladder system that automatically deploys and retracts a ladder from a vehicle, such as an emergency vehicle. The ladder is deployable and retractable with minimal or no human intervention, thereby saving time and/or creating less risk for injury. The ladder is deployed from the rear of a vehicle and rests at an angle on the ground when fully deployed. A two-stage drive unit system is used to deploy and retract the ladder. One drive unit deploys and retracts the ladder on a first rail to a position where the ladder tilts towards the ground. The second drive unit deploys and retracts the ladder from the tilted position to and from the ground on a second rail. Only a partial portion of the ladder&#39;s length is required to be deployed before the ladder will tilt downward towards the ground thereby minimizing open space needed behind the vehicle to deploy the ladder.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to an automatically deployable and retractable ladder device, system, and method for use on vehicles, particularly emergency vehicles.  
       BACKGROUND OF THE INVENTION  
       [0002]     It is common to provide a ladder at the rear of a truck or vehicle, and in particular an emergency related vehicle, for access to the roof. Storage compartments and other necessary items may be stored on top of the vehicle. This type of ladder is commonly referred to as a rear ladder. Most rear ladders are fixedly attached in a vertical arrangement to the rear of the vehicle. The ladder is typically comprised of handrails that are attached and run substantially parallel to the rear of the vehicle with perpendicular steps therebetween. Persons desiring to access the roof of the vehicle scale the ladder until they reach the roof of the vehicle.  
         [0003]     Because these fixedly mounted rear ladders are parallel to the rear of the vehicle, it is more difficult to scale the ladder. The person scaling the ladder is climbing directly upward instead of at an angle, thereby requiring more strength to scale the ladder. Further, because the ladder is vertical, the person scaling the ladder must also support themselves by grabbing the handrails. The person scaling the ladder must not only posses the strength to scale the ladder vertically, but must also balance themselves from falling backward off the ladder.  
         [0004]     Because of these issues, rear-angled ladders have been developed. An angled rear ladder is one where the top of the ladder rests against the rear of the vehicle, and the bottom of the ladder extends outward, away from the vehicle, touching the ground. For example, the ladder may be angled at a 45 degree angle with respect to the ground, as opposed to a 90 degree angle like that of a vertical ladder fixedly attached to the rear of the vehicle. The steps on such rear-angled ladders may encompass the form of steps in a staircase fashion rather than more narrow rods or steps found on a vertical rear ladder. However, many of these rear-angled ladders must be manually deployed. When not deployed, the ladder rests on top or on the roof of the vehicle. When service personnel desires to employ the ladder, the service personnel must access the roof of the vehicle, sometimes through a separate vertical ladder, to retrieve the ladder from storage and deploy the ladder off the rear of the vehicle in an angled manner. Not only can this task be time consuming, but it can also create the potential for injury or other dangers.  
         [0005]     U.S. Pat. No. 5,632,591 (hereinafter the “&#39;591 patent”) discloses one example of automated as opposed to manual deployable and retractable rear ladder system. However, the ladder in the &#39;591 employs a support carriage that must pivot in order to lower the ladder in the rear of the vehicle during deployment. The carriage must pivot, because only one drive system is used to deploy and retract the ladder for both the diagonal and horizontal positions of the ladder. If the pivot arm fails, the ladder cannot be deployed. Further, in the &#39;591 patent, the roof of the vehicle must have enough room to support the entire length of the ladder thereby possibly making it unpractical for shorter length vehicles. During retraction, the ladder is only secured to the roof once the ladder is fully retracted and reaches the hood located towards the front of the vehicle. Further, because the ladder is comprised of one continuous section, the ladder may be unknowingly deployed on the ground at places that are not recognized by service personnel as uneven or not stable until the ladder is traversed thereby creating more potential for accidents.  
         [0006]     Therefore, the object of the invention is to provide an automatic deployable and retractable rear ladder that does not suffer from the aforementioned deficiencies.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is directed to a two-rail rear-angled ladder that is automatically deployable and retractable with minimal or no human intervention, thereby saving time and/or creating less risk for injury. The ladder is deployed from the rear of a vehicle. Only a partial portion of the ladder&#39;s length is required to be deployed before the ladder will tilt downward towards the ground. This minimizes open space needed behind the vehicle to deploy the ladder and reduces safety hazards caused as a result of deploying or retracting a full length ladder.  
         [0008]     The ladder is secured to the roof of the vehicle using a rail system to ensure that the ladder is secured to the roof during the retraction process up and until the ladder is ready to be tilted downward for ground deployment. In order to deploy and retract the ladder of the present invention, a two-stage process is used that employs two separate drive units and two-rail systems to retract the ladder. During deployment, the first or carriage motor drive unit deploys the ladder by driving a carriage along a roof rail system supporting a ladder rail that supports the ladder. The ladder rail is driven outward along a roof rail from the rear of the vehicle from its resting position on and substantially parallel to roof of the vehicle. The ladder and ladder rail are designed to tilt downward after the ladder rail supporting the ladder is partially disengaged from the roof rail.  
         [0009]     Thereafter, a second or ladder motor drive unit attached to the ladder rail deploys the ladder along a second ladder rail system toward the ground at the titled angle away from the vehicle. In this manner, open space required for deployment of the ladder is minimized to prevent accidents caused by deploying and retracting the ladder. Further, by employing the two drive system, the carriage does not have to tilt or pivot to fully deploy the ladder.  
         [0010]     The ladder also contains a bottom section that is hingedly attached to a top section of the ladder. In this manner, the bottom section of the ladder can be flipped onto the top section of the ladder to minimize storage space when using a ladder that may otherwise be too long for the vehicle roof. Further, this allows the top section of the ladder to be fully deployed without the top section touching the ground during the automatic deployment process so that persons do not traverse the latter where the ladder ground contact is unknowingly believed to be stable. After full deployment, the bottom section can be flipped open to engage the ladder with ground in a controlled manner. This decreases the likelihood someone will traverse the ladder without the ladder being coupled to the ground in a stable manner.  
         [0011]     In a second ladder embodiment, two carriage screw shafts rather than one carriage screw shaft are provided to move the carriage along the roof rail. The two carriage screw shafts are provided on each side of a center axis through the carriage drive. In this manner, the carriage screw shafts are moved out of the walking area of the roof of the vehicle. The carriage drive unit drives both the carriage screw shafts at the same time in unison to move the carriage along the roof to deploy and retract the ladder. Providing two carriage screw shafts allows the carriage drive unit to move the carriage and thus the ladder more slowly for greater control during deployment and retraction.  
         [0012]     A handrail and bottom section ladder locking system may also be employed so that these items are securely locked in place when the ladder is deployed and to be used. A spring-loaded dead bolt system is employed. A locking handle is attached to a dead bolt and is used to extend the dead bolt through orifices located on opposite sides of the ladder for the bottom section of the ladder locking system, and through orifices in the handrail posts for the handrails in the handrail locking system. The handle is pushed to lock the deadbolt in place when locking is desired to prevent the bottom section of the ladder and the handrails from being retracted in a storage position.  
         [0013]     Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the invention, and together with the description serve to explain the principles of the invention.  
         [0015]      FIG. 1  is an illustration of the automatically deployable and retractable rear ladder of the present invention when fully deployed;  
         [0016]      FIG. 2A  is a front perspective view illustration of the ladder fully deployed;  
         [0017]      FIG. 2B  is a rear perspective view illustration of the ladder fully deployed;  
         [0018]      FIG. 2C  is a close up illustration of ladder motor drive unit for deploying and retracting the top section of the ladder from a parallel to an angled position with respect to the vehicle roof;  
         [0019]      FIG. 2D  is a top view illustration of the ladder illustrated in  FIGS. 2A-2C ;  
         [0020]      FIG. 3A  is a front perspective view illustration of the ladder raised to an almost parallel position for retraction along the roof rail;  
         [0021]      FIG. 3B  is a bottom perspective view illustration of the ladder illustrated in  FIG. 3A ;  
         [0022]      FIG. 3C  is a side view illustration of the ladder illustrated in  FIG. 3A ;  
         [0023]      FIG. 4A  is a front perspective view illustration of the ladder raised to a parallel position for retraction along the roof rail;  
         [0024]      FIG. 4B  is a side view illustration of the ladder illustrated in  FIG. 4A ;  
         [0025]      FIG. 5A  is a front perspective view illustration of the ladder fully retracted along the roof rail;  
         [0026]      FIG. 5B  is a rear perspective view illustration of the ladder fully retracted along the roof rail;  
         [0027]      FIG. 5C  is a top view of the ladder illustrated in  FIGS. 5A and 5B ;  
         [0028]      FIG. 5D  is a side view of the ladder illustrated in  FIGS. 5A-5C ;  
         [0029]      FIG. 6A  is a front perspective view illustration of an alternative ladder embodiment fully deployed;  
         [0030]      FIG. 6B  is a rear perspective view illustration of the alternative ladder embodiment fully deployed;  
         [0031]      FIG. 6C  is a close up illustration of the ladder motor drive unit for deploying and retracting the top section of the alternative ladder embodiment from a parallel to an angled position with respect to the vehicle roof;  
         [0032]      FIG. 6D  is a top view illustration of the alternative ladder embodiment illustrated in  FIGS. 6A-6C ;  
         [0033]      FIG. 7A  is a front perspective view illustration of the alternative ladder embodiment raised to an almost parallel position for retraction along the roof rail;  
         [0034]      FIG. 7B  is a bottom perspective view illustration of the alternative ladder embodiment illustrated in  FIG. 7A ;  
         [0035]      FIG. 7C  is a side view illustration of the alternative ladder embodiment illustrated in  FIG. 7A ;  
         [0036]      FIG. 8A  is a front perspective view illustration of the alternative ladder embodiment raised to a parallel position for retraction along the roof rail;  
         [0037]      FIG. 8B  is a side view illustration of the alternative ladder embodiment illustrated in  FIG. 8A ;  
         [0038]      FIG. 9A  is a front perspective view illustration of the alternative ladder embodiment fully retracted along the roof rail;  
         [0039]      FIG. 9B  is a rear perspective view illustration of the alternative ladder embodiment fully retracted along the roof rail;  
         [0040]      FIG. 9C  is a top view of the alternative ladder embodiment illustrated in  FIGS. 9A and 9B ; and  
         [0041]      FIG. 9D  is a side view of the alternative ladder embodiment illustrated in  FIGS. 9A-9C .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of practicing the invention. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.  
         [0043]     The drawings of the application illustrate the ladder in its fully deployed position through a retraction process until fully stored on the roof of the vehicle. Thus, deployment of the ladder occurs in reverse and thus the discussion below also inherently discloses the deployment process. An overview of the ladder and the components that allow for its deployment and retraction will be described generally in the description of  FIG. 1  below. The remainder of the application will illustrate the ladder in various views during the retraction process.  
         [0044]      FIG. 1  illustrates a general view of the ladder in its fully deployed position on a vehicle. A vehicle  10  is provided that contains a ladder  12 . The vehicle  10  may be an emergency vehicle including a fire truck, for example. The vehicle  10  includes a roof  14  which is used to support the ladder  12  when retracted and/or other compartments for storage purposes. The ladder  12  is comprised of a plurality of steps  16  that are used to support a person traversing the ladder  12 . The steps  16  may be solid, perforated, and/or stair case type steps  12 . The tops of the steps  16  may contain an anti-slip material or may consist of metal strips having uneven edges to provide a gripping surface to prevent falls when the ladder  12  is being traversed. The ladder  12  is further comprised of two sections. The first section is a bottom section  18 , which is attached to a top section  20  of the ladder  12  via a hinge  21 . In this manner, the bottom section  18  can flip up along the hinge  21  and rest on the top section  20  of the ladder  12 , as will be illustrated later in this application. Providing the bottom section  18  of the ladder  12  that flips upward on the top section  20  allows for a longer ladder  12  to be stored on a shorter length roof  14 .  
         [0045]     The ladder  12  also contains handrails  22  that provide support to persons traversing the ladder  12 . To retract the ladder  12 , the top section  20  of the ladder  12  is pulled along a ladder rail  26  via a ladder motor drive unit  28 . In one embodiment, the ladder motor drive unit  28  is a CDP3430-V12 model ½ HP motor manufactured by BALDOR. The ladder rail  26  is attached to a carriage  24  via a ladder-roof rail coupler  47 . The ladder-roof rail coupler  47  is attached to the ladder rail  26 . The ladder  12  contains rollers  42  that are designed to roll along inside of the ladder rail  26 . When the ladder motor drive unit  28  is activated, the top section  20  of the ladder  12  (and its rollers  42 ) is pulled upward along the ladder rail  26  that guides its retraction upward at the angle of deployment. The rollers  42  may be manufactured out of rubber, plastic, or a hardened material.  
         [0046]     When a portion of top section  20  of the ladder  12  extends sufficiently beyond the ladder rail  26  to tilt downward towards the roof of the vehicle via gravity in a clockwise rotation  30 , the top section  20  of the ladder  12 , and more particularly ladder-roof rail coupler rollers  49  attached to the ladder roof-rail coupler  47 , will fall down into and be supported by a roof rail  32 . The roof rail  32  is mounted to the roof  14  of the vehicle  12  via a roof rail mount  34 . A secondary roof rail  33  is mounted to the roof  14  of the vehicle  12  via secondary roof rail mounts  35 . The ladder  12  is designed so that the top section  20  of the ladder  12  does not tilt downward in a position parallel to the roof  14  during retraction until the front of the top section  12  is adjacent the secondary roof rail  33 . The ladder-roof rail coupler rollers  42  may be manufactured out of rubber, plastic, or a hardened material.  
         [0047]     Thereafter, in a second phase of the retraction process, the ladder  12  is parallel to the roof  14 . A carriage motor drive unit  36 , which is attached to the carriage  24  via a carriage screw shaft  38 , pulls the carriage  24  forward in order to pull the top section  20  of the ladder  12  forward towards the cabin of the vehicle  10  along the roof rail  32 , and into the secondary roof rail  33 . The carriage motor drive unit  36  may be a CDP3430-V12 model ½ HP motor manufactured by BALDOR. The carriage  24  is attached to the ladder-roof rail coupler  47 , which is attached to the ladder rail  26 . Thus, pulling of the carriage  24  pulls the ladder  12  supported inside the ladder rail  26  forward. The carriage motor drive unit  36  is mounted to the roof  14  of the vehicle  12  via a carriage motor drive unit mount  37 . Eventually, as the carriage motor drive unit  36  pulls upon carriage  24  to pull the top section  20  of the ladder  12  forward, the ladder  12  will hit a screw shaft stop  40  to prevent the ladder  12  from being pulled forward any further.  
         [0048]      FIGS. 2A through 2D  illustrate a more detailed view of the ladder  12  in its fully retracted position. As illustrated in  FIGS. 2A through 2D , the handrails  22  of the ladder  12  are comprised of an elongated pipe  44  with curved ends  46  at the top section  20  of the ladder  12 . The elongated pipes  44  are supported by vertical supports  48  that are designed to insert into handrail posts  50  attached to the outer edges of the ladder  12 . The handrail posts  50  contain handrail post hinges  51 , so that the handrail posts  50 , as supporting the vertical supports  48 , can bend at a right angle inward towards the ladder  12  so that the handrails  22  can be placed on top of each other in a resting position, as illustrated in  FIG. 3A  and discussed below. Handrail cross member supports  52  are also provided to allow further structural support for the handrails  22 . Handrail knobs  54  are contained at the top of the vertical supports  48  where they intersect with the elongated pipe  44 , to terminate the ends of the vertical supports  48 .  
         [0049]     The ladder motor drive unit  28  is mounted to the top section  20  of the ladder  12  via a mounting plate  55 . Ladder motor drive unit mounting bolts  58  attach the ladder motor drive unit  28  to the mounting plate  55 . As previously discussed, the ladder motor drive unit  28  is activated to deploy and retract the top section  20  of the ladder  12  along the ladder rail  26  when in a tilted position.  FIG. 2B  illustrates a perspective view of the ladder  12  when fully deployed. Section ‘A’ in  FIG. 2B  is illustrated in more detail in  FIG. 2C , which shows the ladder motor drive unit  28  containing a ladder motor drive unit shaft  56  that supports a ladder motor drive unit chain  57  connected to a ladder motor drive unit sprocket  60  designed to drive a ladder motor drive unit sprocket shaft  59  when the ladder motor drive unit belt chain  57  rotates. As the ladder motor drive unit shaft  56  rotates, the ladder motor drive unit sprocket shaft  59  rotates because of the chain  57  attached to the sprocket  60 . A ladder sprocket chain  61  situated perpendicular to the ladder motor drive unit chain  57  moves as a result, causing a ladder screw shaft sprocket  63  to rotate, thereby rotating a ladder screw drive  65  that will pull the top section  20  of the ladder  12  along the ladder rail  26 .  FIG. 3B  illustrates the aforementioned components from a bottom view perspective.  
         [0050]     Further, as illustrated  FIG. 2C , the carriage  24  is comprised of a carriage base  62  that is coupled to carriage supports  64  that are V-shaped. Carriage rollers  66  are attached via carriage fasteners  68  to ends of the carriage supports  24  for a total of four carriage rollers  66 . The carriage rollers  66  are adapted to fit inside and roll along the roof rail  32  when the ladder  12  is retracted by the carriage motor drive unit  36 . The roof rail  32  contains two roof rail slots  76 . The ladder-roof rail coupler rollers  49  are adapted to fit inside the roof rail slots  76  and inside a roof rail guide  78  to fully couple the ladder  12  to the carriage  24 . The ladder rail  26  contains two tabs  75  on its ends that are adapted to fit inside slots  85  contained in the body of the carriage  24  when the ladder rail  26  tilts downward parallel to the roof  14 . Bumpers  87  are provided to support the ladder rail  26  when the tabs  75  fit into the slots  85 . By coupling the ladder rail tabs  75  into the slots  85  on the carriage  24 , when the carriage  24  is pulled forward, the carriage  24  will also pull the ladder rail  26  forward along the roof rail guide  78 , thereby causing the ladder  12  to move forward on the roof  14  inside the roof rail  32 . The ladder-roof rail couplers  49  roll along inside the roof rail guide  78  as the ladder rail  26  is pulled forward.  
         [0051]     Also as illustrated in  FIG. 2C , the carriage  24  contains strut holders  81  that are designed to prevent struts  79  attached to strut mounts  83  attached to the ladder-roof rail coupler  47  from extending beyond a given tilt angle. In this manner, as the top section  20  of the ladder  12  is deployed and begins to tilt downward via gravity, the struts  79  do not allow the ladder  12  to tilt downward at more of an angle than desired according to the designed length of the struts  79 . The front rollers of the ladder-roof rail coupler rollers  49  are also designed to be located at the roof rail slots  76  when gravity tilts the ladder  12  downward so that a portion of the ladder-roof rail coupler  47  automatically disengages from the roof rail  32  and tilting upward toward the ground at the angle of deployment allowed by the struts  79 . Only the rear ladder-roof rail coupler rollers  47  remain engaged with the roof rail  32  to support the ladder rail  26  and for the ladder  12  to be deployed down the ladder rail  26  to the ground. The rear ladder-roof rail coupler rollers  47  fit inside and are retained inside a cup (not shown) in the roof rail  32  when such rollers  47  reach the back of the roof rail  32  just before the ladder rail  26  pivots.  
         [0052]     Also as illustrated in  FIG. 2C , the carriage  24  contains a carriage screw shaft mount  80  that supports the carriage screw shaft  38  to the carriage  24 . The carriage screw shaft mount  80  contains a threaded orifice that the carriage screw shaft  38  screws into. The carriage screw shaft  38  also attaches into screw shaft fixed end mount  82  mounted to the roof  14  to secure the shaft  38  at the far end. As shown in  FIG. 2D , the carriage screw shaft  38  is attached to the carriage motor drive unit  36 . The carriage motor drive unit  36  causes the carriage screw shaft  38  to rotate. As the carriage screw shaft  38  rotates, the carriage screw shaft mount  80  moves about the carriage screw shaft  38 , thereby moving the carriage  24  forward from the screw shaft fixed end mount  82  towards the carriage motor drive unit  36 . In this manner, by the carriage  24  being attached to the ladder-roof rail coupler  47 , the ladder-roof rail coupler rollers  49  will be moved forward by the rear carriage rollers  66 , thereby moving the top section  20  of the ladder  12  forward as previously described.  
         [0053]      FIG. 2D  illustrates a top view of the ladder  12  in its fully deployed position as an alternative view.  
         [0054]      FIGS. 3A-3C  illustrate various view of the ladder  12  when the top section  20  is fully retracted along the ladder rail  26  and the ladder  12  is ready to tilt downward to be secured inside the roof rail  32 . As illustrated in  FIG. 3A , the bottom section  18  of the ladder  12  has been tilted upward along the hinge  21  to rest on top of the top section  20  of the ladder  12 . Typically, a person will flip up the bottom section  18  before initiating the retraction process, and flip down the bottom section  18  after a deployment process. Also note a person will typically fold the vertical support  48  for the handrails  22  downward before retraction begins. The vertical support  48  are designed to fold along the handrail post hinges  51  located in the handrail posts  50  that attach the vertical supports  48  to the ladder  12 .  
         [0055]     Also note in  FIG. 3A , that the ladder-roof rail coupler roller  49  is just about to fit down inside the roof rail slot  76  so that the ladder-roof rail coupler roller  49  is inside the roof rail  32  and in front of the rear carriage rollers  66  as previously described. The ladder  12  is designed so that the weight of the top section  20  extending forward past the carriage  24  will cause the top section  20  to fall downward towards the roof  14  at a point where the front of the top section  20  of the ladder is adjacent the secondary roof rail  33 . Only the ladder-roof rail coupler rollers  49  fit inside and roll along the roof rail  32 . The ladder rollers  42  ride below the roof rail  32  as the ladder  12  is pulled forward by the carriage motor drive unit  36  pulling the carriage  24  forward.  
         [0056]     The ladder  12  begins to tilt when the about half of the length of the ladder  12  is deployed or retracted, as opposed to ladder systems that require all or substantially all of the length of the ladder to be retracted or deployed before the ladder tilts. The present invention may include variations where the ladder is designed to tilt when the ladder is deployed as little as 10% of its entire length or up to 90%. Conversely stated, the ladder is retracted when only 90% of the ladder is retracted down to 10%. The closer the percentage to 50% of the ladder  12  (or top section  20 ) length, the less open space will be required in the rear of the vehicle to deploy and retract the ladder  12 .  
         [0057]      FIG. 3B  illustrates a bottom perspective view of the ladder  12  in a partially retracted or deployed state, and is further illustrated in  FIG. 3A  to better illustrate certain components. Note that the ladder screw shaft  65  is fixedly attached to the ladder  12  via a ladder screw shaft fixed end mount  77 . The ladder screw shaft  65  is also attached to a ladder screw shaft traverse mount  69 . In this manner, the ladder motor drive unit  28  causes the ladder screw shaft  65  to rotate and move the ladder  12  up and down about the ladder screw shaft traverse mount  69 , similar to the design of the carriage screw shaft mount  80  as previously described above. A ladder cross member  73  is attached perpendicular to the ladder rail  26  on its end as support for the ladder rail  26 .  
         [0058]      FIG. 3C  illustrates the ladder  12  in the partially deployed or retracted state in  FIGS. 3A and 3B  from a side view simply to provide an alternative illustration.  
         [0059]      FIGS. 4A-4B  illustrate the ladder  12  when the top section  20  is fully parallel to the roof  14 . This occurs when either gravity pulls the top section  20  downward during retraction, or after the ladder  12  is initially deployed outward by the carriage motor drive unit  36  before the opposite end of the top section  20  and bottom section  18  tilt downward. As can be seen, the ladder-roof rail coupler rollers  49  are fully engaged and inserted inside the roof rail  32 . Thus, the carriage motor drive until  36  can pull the carriage  24  to in turn pull the top section  20  of the ladder  12  forward for retraction.  
         [0060]      FIGS. 5A-5D  illustrate the ladder  12  in a fully retracted state. Note that the top section  20  of the ladder  12  is fully retracted forward adjacent the carriage motor drive unit  36 . The secondary roof rail  33  supports the ladder rollers  42 . The secondary roof rail  33  is located in a lower plane than the roof rail  32  since the ladder rail rollers  42  are located in a lower plane than the ladder-roof rail coupler rollers  49  that ride inside the roof rail  32 .  
         [0061]      FIGS. 6A-6D  illustrate an alternative embodiment of the ladder  12  similar to the ladder illustrated in  FIGS. 2A-5D . The common components between the two ladder systems are labeled with the same numbers. In the ladder  12  illustrated in  FIG. 6A , bearing mounts  100  are provided along the roof  14  to support pillow block bearings  101  that carry  102 A and  102 B carriage drive screws. Two carriage screw shafts  102 A,  102 B as opposed to one screw drive shaft is provided. The two carriage screw shafts  102 A,  102 B are provided on each side of a center axis through the carriage motor drive unit  36  where the screw drive shaft  38  was provided in the ladder  12  of  FIGS. 2A-5D . In this manner, the carriage screw shafts  102 A,  102 B are moved out of the walking area of the roof  14 .  
         [0062]     The rotating shaft  104  out of the carriage motor drive unit  36  is coupled to two chains  106 A,  106 B, one chain for each sprocket  108 A,  108 B for each carriage screw shaft  102 A,  102 B. In this manner, the carriage motor drive unit  36  drives both the carriage screw shafts  102 A,  102 B at the same time in unison to move the carriage  24  along the roof  14  to deploy and retract the ladder  12 . The carriage screw shafts  102 A,  102 B are fixedly mounted to carriage screw shaft fixed end mounts  114  attached to the bearing mounts  100  located farthest from the carriage motor drive unit  36 . The carriage  24  also provides two carriage screw shaft mounts  110 , one for each carriage screw shaft  102 A,  102 B. The carriage screw shaft mounts  110  contain threaded orifices  112  about which the carriage screw shafts  102 A,  102 B are inserted and rotate about to move the carriage  24  up and down the carriage screw shafts  102 A,  102 B.  
         [0063]      FIG. 6B , a perspective rear view of the ladder  12  illustrated in  FIG. 6A , illustrates an alternative locking system for the lower portion  18  of the ladder  12  so that the lower portion  18  is locked in place when extended about the hinge  21  to an extended position. As illustrated in  FIG. 6B , a spring-loaded dead bolt system is employed. A locking handle  126  is attached to a dead bolt  127  and is used to extend the dead bolt  127  (illustrated in  FIG. 6A ) through orifices  129  located on opposite sides of the ladder  12 . In this manner, when the lower portion  18  is extended from the top section  20  of the ladder  12 , the locking handle  126  is engaged or pushed to extend the dead bolt  127  through the orifice  129  on the opposite side of the locking handle  126 . In this manner, the lower portion  18  is locked into place and cannot be folded or retracted back onto the top section  20  of the ladder  12  as a safety feature. When the lower portion  18  is desired to be retracted, the locking handle  126  is pulled to retract the dead bolt  127 , which will allow the lower portion  18  to be folded about hinge  21 .  
         [0064]     The alternative ladder embodiment also contains a locking system for the handrails  22  similar to that of the lower portion  18  of the ladder  12 . As illustrated in  FIG. 6B , a spring-loaded locking handle  128  is provided that is attached to a dead bolt  130 . The dead bolt  130  extends through orifices  132  provided through the vertical supports  48  of the handrails  22 . When it is desired to extend the handrails  44  upright and lock them into place, the locking handle  128  is rotated to release energy in a spring (not shown) which pulls the dead bolt  130  up the ladder to extend into an ending orifice  131 . The locking handle  128  in effect is spring-assisted. When the dead bolt  130  is extended through the end orifice  131 , its blocks its proximate vertical support  48  from folding inward by blocking the handrail post hinge  51 . In this manner, the handrails  22  will not accidentally fall downward when in use. When it is desired to retract the handrails  22  to lay down on top of the ladder  12  when it is to be retracted, the locking handle  128  is pulled against the spring to retract the dead bolt  130  from the end orifice  131 , which allows the vertical support  48  to be rotated about the handrail post hinge  51 . The locking handle  128  is rotated to lock the energy in the spring in place so that it can be released to provide spring-assistance when locking is desired, as discussed above.  
         [0065]     Another difference is provided in the linkage between the ladder-roof rail coupler  47  and the carriage  24  that controls the maximum tilt angle of the ladder rail  26  and thus the ladder  12  when retracted. In the ladder  12  of  FIGS. 2A-5D , struts  79  are provided that are fixedly attached to strut mounts  83  on the ladder-roof rail coupler  47 , and slidably linked to strut holders  81  attached to the carriage  24 . In the alternative ladder embodiment, as illustrated in  FIG. 6C , a close up view of the carriage  24 , a linkage having fixedly attached ends on both the carriage  24  and the ladder-roof rail coupler  47  is provided. This allows the carriage  24  movement to control the speed at which the ladder-roof rail coupler  47 , and thus the ladder rail  26  and ladder  12 , pivots to tilt downward before the ladder  12  is deployed towards the ground.  
         [0066]     As illustrated in  FIG. 6C , a fixed strut  116  is provided to attach the ladder-roof rail coupler  47  to the carriage  24 . The fixed strut  116  is fixedly attached to the ladder-roof rail coupler  47  by strut holders  81 . The fixed strut  116  is also fixedly attached to the carriage  24  using a carriage bolt  120  placed through an orifice  122  in the fixed strut  116 .  
         [0067]     The fixed strut  116  contains two grooves  119 ,  124  on each end. Before the ladder  12  has begun to tilt downward during deployment, the grooves  119 ,  124  are coupled with carriage bolts  126 ,  127  to allow the fixed strut  116  to rest in a parallel position to the roof  14  when the ladder  12  is parallel to the roof  14  inside the roof rail  32 . When the carriage motor drive unit  36  rotates the carriage screw shafts  102 A,  102 B to deploy the ladder  12 , and when the ladder-roof rail coupler rollers  49  move underneath the roof rail slots  76  and are released, the ladder-roof rail coupler  47  is fixedly held by the fixed strut  116 . Only by the carriage  24  continuing to be moved outward is the ladder-roof rail coupler  47  allowed to move upward to tilt the ladder rail  26  and ladder  12  downward. The speed at which the carriage motor drive unit  36  rotates the carriage screw shaft  102 A,  102 B controls the speed at which the ladder rail  26  is tilted. Gravity pulling on the ladder rail  26  does not control the speed at which the ladder rail  26  is tilted in this embodiment unlike the ladder  12  illustrated in  FIGS. 2A-5D . The ladder rail  26  is only allowed to be tilted according to the distance the carriage  26  is moved in combination with the length of the fixed strut  116 .  
         [0068]      FIG. 6D  illustrates a top view of the alternative ladder embodiment of the ladder in  FIGS. 6A-6C  in its fully deployed position as an alternative view.  
         [0069]      FIGS. 7A-7C  illustrate various views of the alternative ladder  12  embodiment when the top section  20  is fully retracted along the ladder rail  26  and the ladder  12  is ready to tilt downward to be secured inside the roof rail  32 . As illustrated in  FIG. 3A , the bottom section  18  of the ladder  12  has been tilted upward along the hinge  21  to rest on top of the top section  20  of the ladder  12 . Typically, a person will flip up the bottom section  18  before initiating the retraction process, and flip down the bottom section  18  after a deployment process. Also note a person will typically fold the vertical supports  48  for the handrails  22  downward before retraction begins. The vertical support  48  are designed to fold along the handrail post hinges  51  located in the handrail posts  50  that attach the vertical supports  48  to the ladder  12 .  
         [0070]     Further note in  FIG. 3A , that the ladder-roof rail coupler roller  49  is just about to fit down inside the roof rail slot  76  so that the ladder-roof rail coupler roller  49  is inside the roof rail  32  and in front of the rear carriage rollers  66 , as previously described. The ladder  12  is designed so that the weight of the top section  20  extending forward past the carriage  24  will cause the top section  20  to fall downward towards the roof  14  at a point where the front of the top section  20  of the ladder is adjacent the secondary roof rail  33 . Only the ladder-roof rail coupler rollers  49  fit inside and roll along the roof rail  32 . The ladder rail rollers  42  ride below the roof rail  32  as the ladder  12  is pulled forward by the carriage motor drive unit  36  pulling the carriage  24  forward.  
         [0071]     The ladder  12  begins to tilt when the about half of the length of the ladder  12  is deployed or retracted, as opposed to ladder systems that require all or substantially all of the length of the ladder to be retracted or deployed before the ladder tilts.  
         [0072]      FIG. 7B  illustrates a bottom perspective view of the alternative ladder  12  embodiment in a partially retracted or deployed state. Note that the ladder screw drive  65  is located in approximately the center of the long axis of the ladder  12 .  
         [0073]      FIG. 7C  illustrates the ladder  12  in the partially deployed or retracted state in  FIGS. 7A and 7B  from a side view simply to provide an alternative illustration.  
         [0074]      FIGS. 8A-8B  illustrate the alternative ladder  12  embodiment when the top section  20  is fully parallel to the roof  14 . This occurs when the carriage motor drive unit  36  pulls the carriage  24  forward, which in turn causes the fixed strut  116  to pull on the ladder-roof rail coupler  47  and ladder rail  26  downward in a clockwise direction until the ladder-roof rail coupler  47  is engaged with the roof rail  32  and the ladder rail  26  is parallel to the roof  14 . As can be seen, the ladder-roof rail coupler rollers  49  are fully engaged and inserted inside the roof rail  32 . Thus, the carriage motor drive unit  36  can pull the carriage  24  to in turn pull the top section  20  of the ladder  12  forward for retraction.  
         [0075]      FIGS. 9A-9D  illustrate the alternative ladder embodiment with the ladder  12  in a fully retracted state. Note that the top section  20  of the ladder  12  is fully retracted forward adjacent the carriage motor drive unit  36 . The secondary roof rail  33  supports the ladder rollers  42 . The secondary roof rail  33  is located in a lower plane than the roof rail  32 , since the ladder rail rollers  42  are located in a lower plane than the ladder-roof rail coupler rollers  49  that ride inside the roof rail  32 .  
         [0076]     Note that the ladder  12  and the support components, including but not limited to the carriage  24 , ladder rail  26 , roof rail  32 , secondary roof rail  33 , handrails  22  and other components, may be manufactured out of any type of material, including metal, steel and aluminum as examples. The motor drive units  28 ,  36  may be any type of motor drive unit, including AC or DC driven. The motor drive units  28 ,  36  may be screw drive shafts, or may be designed to retract the ladder  12  using chains and sprockets or any other type of pulling and pushing system.  
         [0077]     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present invention. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.