Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is an original non-provisional application claiming benefit of U.S. Provisional Application 60/765,766, filed Feb. 6, 2006, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an automatic retractable ladder that is installed on an access panel hinged on a framing structure that surrounds an opening into the ceiling for access to an attic space. The access panel and the retractable ladder have two positions. In the first position the access panel automatically closes the opening into the ceiling and the retractable ladder is stowed or retracted on top of the access panel, i.e. in the attic. In the second position the access panel automatically uncovers the opening of the ceiling and the retractable ladder automatically deploys or extends to reach the ground. The automatic opening of the access panel and the automatic deploying of the retractable ladder are achieved through gravity, without assistance of a motorized apparatus, after the release of safety latches. The automatic closing of the access panel and the automatic stowing of the retractable ladder are achieved through a single motorized apparatus. The latching of the access panel in its closed position is achieved automatically and mechanically.  
         [0004]     2. Description of the Related Art  
         [0005]     Ladders for attic access are widely used by the people in their private homes. Attic accesses are usually provided above the garages and/or living quarters of private homes. The most common attic access consists of an access panel, spring loaded in the closed position and hinged on a wooden structure frame surrounding an opening in the ceiling and installed in the ceiling. To get access to the attic, a user would pull on a piece of rope attached to -the panel and hanging therefrom. This opens the panel, giving access to a folded ladder. The ladder is usually composed of three sections that are folded on top of each other and hinged between each other. The first section is attached to the panel. To deploy the ladder, a user needs to manually grasp the folded second and third sections, rotates this assembly to the deployed position and finally grasp the third section to manually unfold it from the second section. Once the unfolding is achieved, the three sections of the ladder are usually extended in alignment enabling a user to access the attic space. The opposite process needs to be followed by the user for the refolding of the ladder. For re-closing the panel, the user needs to push firmly on the panel moving the panel up to a couple of inches from the ceiling. At such point the springs of the panel take over and move the panel to its fully closed position.  
         [0006]     The experience shows that the drawbacks of these attic access systems reside in the difficulty of the steps that need to be performed for the opening of the panel, i.e., the unfolding of the ladder, the refolding of the ladder and the re-closing of the panel. While the procedure appears to be easy for a male, provided he is tall, strong and not impaired, the procedure is difficult for a female and virtually impossible as well as potentially dangerous to any elderly person.  
         [0007]     U.S. Pat. No. 6,866,118 describes a ladder that can be extended and retracted by an electric motor. While the technology described appears to be an improvement over the manual attic ladders mentioned previously, its complexity makes it impracticable and too costly for industrial or private home applications.  
         [0008]     It would consequently be of great advantage to provide a system giving easy and safe attic access to everyone at a low cost.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     The present invention overcomes the drawbacks of the prior art by providing a fully automatic access to an attic. More particularly, the invention is composed of an access panel that is hinged towards the forward end of a frame structure that supports sections of ladders. The frame structure supports in its aft end part of the mechanism that unlatches the panel, controls its opening, controls the deployment of the sections of ladders, retracts the ladder and closes the panel and re-latches it on the fixed frame. More particularly, while the invention uses gravity for the opening of the panel and for the extension of the sections of ladders, it uses a single electric motor mounted at the aft end of the framing structure for performing the retraction of the ladders and the closing of the panel. The relatching of the panel and its associated sections of ladders in the stowed position is purely mechanical, i.e., without the assistance of electric energy.  
         [0010]     The stow latch performs the function of maintaining the panel and its associated sections of ladders in the closed position.  
         [0011]     The safety latch performs the function of controlling the opening of the panel and the extension of the sections of ladders to the ground.  
         [0012]     The single electric motor performs two distinct functions. The first function is to retract the sections of ladders to their stowed position after they have been extended to the ground, and the second function is to close the panel.  
         [0013]     In one exemplary embodiment of the invention, there is one electric solenoid for controlling the unlatching of the stow latch and one electric solenoid for controlling the unlatching of the safety latch. Both latches are equipped with a manual override. In another embodiment of the invention, the unlatching of both latches is only achieved manually.  
         [0014]     It is a characteristic of this invention that the electric motor is only energized to retract the sections of ladders and to close the panel to its stowed position. The electric motor is not energized to either open the panel, or to extend the sections of ladders, or to maintain the panel in its stowed position. The shaft of the electric motor is equipped with a gear that drives a single gear free-wheel. The single gear free-wheel is free to rotate in one direction and is driven by the electric motor in the opposite direction. The single gear free-wheel is mechanically connected to two concentric shafts, the inner shaft being supported by the framing structure while the outer shaft supports one spool on each end thereof. The outer shaft is free to rotate in one direction and is driven by the electric motor in the opposite direction. One end of the cables is rolled up on, and attached to, each of the spools. The other extremity of the cables is attached to the last section of the ladder. In the free direction of rotation of the outer shaft, the spools unroll their dedicated cables allowing the opening of the access panel and subsequently the deployment of the sections of ladders. In the other direction of rotation of the shaft, the spools roll up the cables allowing the retraction of the sections of ladders and lastly the closing of the access panel.  
         [0015]     In one embodiment of the invention there is an automatic mechanical locking of the access panel in its fully opened position, once the sections of ladders have departed from their fully retracted position. This is to require the re-stowing of the ladder before the closing of the panel.  
         [0016]     In another embodiment of the invention, there is no mechanical locking of the access panel in its fully opened position.  
         [0017]     The ladder of the invention is at least composed of two distinct sections that are engaged in a sliding arrangement. Depending of the height of the ceiling, the number of sections can be increased. The figures accompanying the detailed description of the invention show three sections of ladders. The first ladder section is mechanically attached to the access panel, the second ladder section is arranged to slide on top of the first ladder section, and the third ladder section is arranged to slide on top of the second ladder section. Mechanical stops are provided on each of the ladder sections for limiting the sliding stroke.  
         [0018]     The invention, in accordance with preferred and exemplary embodiments, together with further objects and advantages thereof, is more particularly described in the following detailed description taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a perspective view of an access panel shown in its stowed position;  
         [0020]      FIG. 2  is a perspective view of the access panel shown in  FIG. 1  with the framing structure removed;  
         [0021]      FIG. 3  is a perspective view of the framing structure equipped with a driving mechanism;  
         [0022]      FIG. 4  is an enlarged partial perspective view of the rear portion of the framing structure shown in  FIG. 3  and the driving mechanism;  
         [0023]      FIG. 4   a  is an enlarged perspective view of a portion of the apparatus shown in  FIG. 4  for unrolling and rolling the cables;  
         [0024]      FIG. 4   b  is an enlarged partial perspective view of the brake shown in  FIG. 4 ;  
         [0025]      FIG. 5  is an enlarged perspective view of the stow latch of the apparatus in the latched and stowed position;  
         [0026]      FIG. 6  is a side view of the access panel shown in the opened position, with sections of the ladder being retracted, hidden items being shown in dotted lines;  
         [0027]      FIG. 7  is a side view of the access panel showing full extension of section  2  and partial extension of section  3 , with the access panel being locked in its opened position;  
         [0028]      FIG. 8  shows a perspective view of the access panel in its fully extended position;  
         [0029]      FIG. 9  shows perspective view of the first ladder section;  
         [0030]      FIG. 10  shows a perspective view of the second ladder section;  
         [0031]      FIG. 11  shows a perspective view of the third ladder section; and  
         [0032]      FIG. 12  is a partial perspective view of the first ladder section and the cover of the access panel;  
         [0033]      FIG. 13  is a partial side view of a different braking system with the ladder section removed and the access panel being closed; and  
         [0034]      FIG. 14  is a partial side view of  FIG. 13  with the ladder sections removed and the access panel being open.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof and are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is understood that other embodiments may be utilized without departing from the spirit or scope of the invention. To avoid detail not necessary to enable those skilled in the art to practice the invention, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.  
         [0036]     With reference to  FIG. 1 , the ladder sections  500 ,  600 ,  700  of access panel  30  are shown in their retracted and stowed position. The ladder sections  500 ,  600 ,  700  are mounted on a frame structure  10 . With reference to  FIG. 2  where the framing structure  10  is removed for clarity, the first ladder section  500  is spaced away from the inner surface  810  of the cover  800  (See  FIG. 12 ). Beams  801  are mechanically attached to the cover  800 . In this manner, the climbing of the steps of ladder  500  is not affected by the presence of the cover  800 . In other words, the resting position of the feet of the user of the ladder portions of the access panel  30  remains the same whether the user is on ladder sections  700 ,  600  or  500 . This allows each step of the ladder sections to have the same depth, and this provides to the user the same position of steps against his feet regardless of which section of the ladder he is standing on.  
         [0037]     There are many manual retractable ladders that are commonly used in the industry, and more particularly in the construction industry. These ladders are composed of different sections that are arranged to slide on one another so that they can be extended and retracted. However the steps of these ladders are usually composed of a plurality of rungs. Such a step configuration would be neither comfortable nor safe for everyone to use. Therefore, as shown on  FIGS. 2, 9 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11 , and  12 , all the steps have a comfortable width for the security of the person climbing of each of the sections.  
         [0038]     With reference to  FIG. 2  the ladder sections  500 ,  600 ,  700  are configured to allow a longitudinal sliding motion between each other. Section  500  is mechanically attached to cover  800  and spaced from it by beams  801 . Section  600  is configured to slide longitudinally on top of, but inside, section  500 . Section  700  is configured to slide longitudinally on top of, but outside, section  600 . No further description of the sliding arrangement is made as this is a very well known and used in industrial ladders technology.  
         [0039]     Cover  800  that supports the ladder sections  500 ,  600 ,  700  is hinged via hinge  819  on forward end  13  of the framing structure  10  (See  FIGS. 1 and 2 ). Since ladder section  500  is mechanically attached to cover  800 , the hinge  819  can alternatively be installed between ladder section  500  and forward end  13  of framing structure  10 .  
         [0040]     Still in reference to  FIG. 2 , one end of cables  50  is attached to reels  101  while their other end is attached to bars  703  of ladder section  700 . Cables  50  are guided by pulleys  301  hinged on the framing structure  10  (See  FIG. 1 ), the pulleys  303  hinged on cover  800  and pulleys  305  hinged on ladder section  500 . Clevis supports  304  of pulleys  303  are located such that the portion of the cables  50  that is guided by pulleys  301  and  303  is substantially vertical. This decreases the force required for the closing of the cover  800 . Pulleys  305  are supported by clevis fittings  306  that are mechanically attached to either the forward portion of ladder section  500  or the forward portion of the cover  800 . Retainer cables  60  have one end attached to bolts  19  that are mechanically attached to longitudinal sides  11  and  12  of framing support  10  (See  FIG. 3 ). The other end of cables  60  is hinged on clevis fitting  802  that is mechanically attached to the cover  800 .  
         [0041]     Still in reference to  FIG. 2 , the locks  201  have been moved away from their locked position by the rod  704  that is mechanically attached to ladder section  700 . The locks  201  are spring loaded via springs  202  towards their locked position, and their function is to lock the cover  800  to its full opened position when the ladder sections  600  and/or  700  have moved away from their retracted position.  
         [0042]     With reference to  FIG. 3 , the framing structure  10  that supports the ladder sections  500 ,  600 ,  700  has a forward end  13 , a intermediate distal end  14  and an aft end  15 . The three ends  13 ,  14 ,  15  are bordered by two identical longitudinal opposite sides  11  and  12 . There is a central through opening  17  disposed between the forward end  13  and intermediate distal end  14  and the longitudinal sides  11  and  12 . There is no central through opening between intermediate distal end  14  and aft end  15  and the longitudinal sides  11  and  12 ; however, there is a cavity  20  that has a floor  16 . This cavity  20  houses the latching system (as will be subsequently described), the safety system and the driving mechanism  100  of the apparatus of the invention. Still in reference to  FIG. 3 , the forward end  13  provides the support for locks  201 , the function of which is described later. The longitudinal sides  11  and  12  support the driving shafts of the braking system  102 , the devices  302  which support pulleys  301 , and the bolts  19  of the retainer cables  60  ( FIG. 2 ). The lower faces of the longitudinal walls  11  and  12  and of the forward end  13  and intermediate distal end  14  are fitted with a seal  18  that is sandwiched by cover  800  when in its closed position. In this manner, should the access panel  30  be installed in a ceiling of a room that has a atmospheric controlled environment, energy spending is minimized.  
         [0043]     With reference to  FIG. 6 , the cover  800  is shown in its full opened position. Cover  800  cannot open further because it is retained by cables  60 . Pulled by springs  202 , the mechanical locks  201  have started to pivot on mounting devices  203  that are mechanically attached to forward end  13 . One end  205  of the springs  202  is attached to the locks  201  while the other end  206  is attached to rod  503  of ladder section  500  (See  FIG. 9 ). In this position the mechanical locks  201  have hot yet reached their latched position because the ladder section  700  has not moved away from its retracted position.  
         [0044]     With reference to  FIG. 7 , the mechanical locks  201  are pulled by springs  202  and have reached their latched position. The mechanical locks  201  are resting on their abutment fitting  204  that is mechanically attached to the forward end  13 . The mechanical locks  201  are also resting on fittings  501  (See  FIG. 9 ). In this position, the cover  800  and the ladder sections  500 ,  600 ,  700  are locked in the opened position because of the over center arrangement of the mechanical locks  201 . Also in this position, the reaction force that the ladder section  500  communicates to the mechanical locks  201  is to further rotate the mechanical locks  201  towards an even more secure locked position, but this not possible as the abutment fittings  204  prevent the mechanical locks  201  from rotating further.  
         [0045]     In reference to  FIG. 8 , the ladder sections  600  and  700  are fully extended. Cables  60  prevent further opening of cover  800 . Operation of cables  50  with pulleys  301 ,  303  and  305  and reels  101  retract the ladder sections  600  and  700  and close the cover  800  as will be described hereinbelow.  
         [0046]     Starting with  FIG. 1 , the access panel  30  is retracted and closed or stowed. To initiate the opening of the cover  800  of the access panel  30 , one needs to press a switch in the living area (not shown) for energizing of the solenoid  223  that has its piston rod spring loaded in the retracted position (See  FIG. 5 ). This action extends the piston rod of the solenoid  223  which then pivots the unlatching lever  221  of stow latch  225  towards its unlatched position. The unlatch lever  221  disengages stow latch  225  from its latch receptacle  220  mounted on the intermediate distal end  14  of the framing structure  10 , and by gravity the cover  800  moves away from its latched position, but is stopped by the safety latch  211  that engages teeth of latch wheel  210 , which is mechanically attached to one of the reels  101  (See  FIG. 4 ). Energizing the solenoid  213  retracts its piston rod which pivots the safety lever  211  around its axis that is supported by clevis fitting  212 . The piston rod of solenoid  213  is spring loaded in the extended position. Therefore, energization of the solenoid  213  must be maintained for the safety latch  211  to disengaged from the teeth of the wheel  210 . The switch (not shown) that energized the solenoid  213  is a not an ON-OFF switch, but a switch that needs to be pressed and maintained pressed by the user to open the cover  800  and lower ladder sections  600  and  700 . This is a safety characteristic of the invention, as the access panel  30  cannot accidentally fully open and fully extend unless the user has decided to do so. For example, this prevents the full opening of the access panel  30  and extension of the ladder sections  600  and  700 , should solenoid  223  be accidentally energized by a child or anyone else or should the stow latch  225  break. In the event of an electrical failure, the stow latch  225  can be manually released by pulling on rope or chain  151  that goes through the floor  16  of the framing structure  10  (See  FIGS. 3, 4 ,  5  and  6 ). Safety latch  211  can be manually released by pulling on rope or chain  152  (See  FIGS. 4 and 6 ).  
         [0047]     Once stow latch  225  is released and safety latch  211  is kept away from engaging the teeth of latch wheel  210 , by gravity only, without energizing motor  109 , the cover  800  and the ladder sections  500 ,  600 ,  700  keep on opening until the access panel  30  is fully opened to the position shown in  FIG. 6  is reached. During this phase of the opening, it is gravity only that unrolls the cables  50  from their reels  101 . Cover  800  has cables  60  to limit the opening of the panel access  30  to a predetermined angle typically ranging between  60  and  70  degrees. Still in reference to  FIG. 6 , mechanical locks  201  are pulled by their associated springs  202  that force the mechanical locks  201  to rotate around the pivoting axis of mounting devices  203  attached to forward end  13  of framing structure  10 . The pivoting of mechanical lock  201  is also guided and limited by rods  704  attached to ladder section  700  (See  FIGS. 6 and 11 ). In the position shown in  FIG. 6 , the mechanical locks  201  have not reached their locked position because they are still resting on rods  704  and are not resting on fittings  501  of ladder section  500 .  
         [0048]     Gravity effect on ladder sections  600  and  700  continues to unroll cables  50  from reels  101  until the ladder sections  600  and  700  reach the position shown in  FIG. 7 . The stops  603  of ladder section  600  (See  FIG. 10 ) rest on step  740  of ladder section  700 , so that when ladder section  700  is extending from the position of  FIG. 6  to the position shown in  FIG. 7 , ladder section  600  follows in unison with ladder section  700 . In the position of  FIG. 7 , the stops  602  of ladder section  600  (See  FIG. 10 ) rest on the stops  502  of ladder section  500  (See  FIG. 9 ) and, consequently, ladder section  600  has reached its fully extended position. As is also shown in  FIG. 7 , the mechanical locks  201  are no longer resting on rods  704  of ladder section  700  as mechanical locks  201  are pulled by associated springs  202  to their fully locked position. Mechanical locks  201  are now resting on fittings  501  of ladder section  500  (See  FIG. 9 ) and on abutment fittings  204 . In this position the cover  800  and its associated ladder sections  500 ,  600  and  700  are locked open and cannot be closed.  
         [0049]     Gravity effect of ladder section  700  continues to unroll cables  50  from their reels  101  until stops  702  reach stops  604  of ladder section  600  (See  FIG. 10 ). In this position the ladder sections  500 ,  600  and  700  have reached their fully extended position shown in  FIG. 8 . In order to slow down the speed of opening of the cover  800 , and the speed of extension of the ladder sections  500 ,  600  and  700 , a braking system  102  is installed on one of the reels  101  as will be described hereinbelow.  
         [0050]     In reference to  FIGS. 4 and 4   b  the longitudinal wall  12  of framing structure  10  is equipped with a braking system  102  that slows down the rotational speed of the reels  101  when the reels  101  unroll the cables  50  for the opening of the cover  800  and the extension of the ladder sections  500 ,  600 ,  700 . The braking system  102  consists of a free wheel  162  whose inner shaft  150  is part of a flange  161  that is mechanically attached to side wall  12 . The free wheel  162  supports a braking disk  163 . The free wheel  162  is mounted such that it is not free to turn when the free wheel  110  is free to turn i.e., when the free wheel  110  is allowing the reels  101  to unroll the cables  50 . In other words the free wheel  162  of the braking system  102  of the reels  101  is mounted in the opposite way compared to the free wheel  110 . The friction force of reel  101  against braking disc  163  is adjusted through nuts  105  (See  FIG. 4 ).  
         [0051]     As shown in  FIGS. 8 and 11 , ladder section  700  is equipped with adjustable legs  730 , fitted with rotating shoes  731  to ensure perfect contact with the ground when the ladder sections are fully extended.  
         [0052]     As previously described, the opening of the cover  800  and the extending of the ladder sections  500 ,  600 ,  700  is only achieved through gravity. The retraction of the ladder sections  500 ,  600 ,  700  and the closing of the cover  800  is achieved via the assistance of a motor. Starting from the position shown in  FIG. 8 , the motor  109  shown in  FIGS. 4 and 5  is energized via a switch (not shown) in the living area that closes the circuit of the electrical connections of the motor  109  to an electrical power source (not shown). No further description of this is provided as this is very well known in the art. Pinion  108  mounted on the shaft of the motor  109  drives a chain  107  that, is connected to a single gear free wheel  110 . A single gear free wheel  110  is driven by the chain  107  in only one direction of rotation, but is free to rotate in the opposite direction to unroll the cables  50 . The driven rotation of single gear free wheel  110  corresponds to rolling cables  50  on their respective reels  101 . As shown in  FIGS. 4 and 4   a  one of reels  101  is connected to the single gear free wheel  110  via a plurality of fixed rods  11   1 , while the other reel  101  is connected to single gear free wheel  110  via a plurality of adjustable rods  103  and  104 , the adjustment being carried out through nuts  105 . The single gear free wheel  110  is mechanically attached to a center shaft  106  that is supported by the longitudinal walls  11  and  12  of the framing structure  10 .  
         [0053]     The motorized drive of the single gear free wheel  110  in the direction of rolling up the cables  50  on their respective reels  101  continues until the ladder section  700  reaches the position shown in  FIG. 7 . At such point, step  740  of ladder section  700  (See  FIG. 11 ) meets with stops  603  of ladder section  600  (See  FIG. 10 ). Thereafter, further reeling in of cables  50  further retracts ladder section  700  and pulls with it ladder section  600  towards their retracted position. When ladder section  700  approaches its fully retracted position, its rods  704  meet with locks  201  and drives locks  201  towards the unlatched position. At such point as the position shown in  FIG. 6  is reached, the ladder sections  500 ,  600 ,  700  are fully retracted, but the cover  800  is unlatched and ready to be closed by the further rolling up of the cables  50  on their reels  101  to reach the closed position. When the cover  800  is approaching the closed position, stow latch  225 , via spring  224 , meets its latch receptacle  220  (See  FIG. 5 ) forcing stow latch  225  to re-latch. During the complete rolling up sequence of the cables  50 , the teeth of the latch wheel  210  rotate the safety latch  211  away from its latching position (See  FIG. 4 ). Once the access panel  30  is fully re-latched, it is in the configuration shown on  FIGS. 1 and 2  and the electric motor is automatically de-energized, via known means such as electrical load currents for example.  
         [0054]     During the complete retraction of the ladder sections  500 ,  600 ,  700  and the closing of the cover  800 , the braking system  102  offers no resistance as it is free to rotate in the direction of rolling up the cables  50 .  
         [0055]     In reference to  FIGS. 9, 10 , and  11  ladder sections  500 ,  600 ,  700  are respectively fitted with a series of steps  520 ,  620 ,  720  that provides comfort and safety to the user. For instance the steps  520 ,  620 ,  720  may be covered with a non slippery surface. In addition for ease of climbing, ladder sections  500 ,  600  are respectively fitted with railing  505 ,  605  (See  FIGS. 9 and 10 ).  
         [0056]     The invention uses only the motor  109  to retract the ladder sections  500 ,  600 ,  700  and close the cover  800 . Only gravity is used to open the cover  800  of access panel  30  and extend the ladder sections  500 ,  600 ,  700  as previously described.  
         [0057]      FIG. 13  shows the cover  800  on which the ladder sections  500 ,  600 ,  700  (not shown for clarity) are mechanically attached and in their stored position adjacent longitudinal side  1 l. Longitudinal side  11  is equipped with at least one off center pivoting cam  1010  on axis  1020  and a fixed cam  1000 . Pivoting cam  1010  can either take the off center position shown in  FIG. 13 , or the off center position shown on  FIG. 14 . The cable  50 , through the weight of the cover  800  and ladder sections  500 ,  600 ,  700 , produces counter clockwise pivoting motion MI that forces off center pivoting cam  1010  to stay in its position shown in  FIG. 13 . Cable  50  is free, i.e., not squeezed between off center pivoting cam  1010  and fixed cam  1000 .  
         [0058]     In  FIG. 14 , the ladder sections  500 ,  600 ,  700  have started their deployment and cable  50 , through gravity, produces clockwise pivoting motion M 2  to the off center pivoting cam  1010  which makes it rotate around axis  1020  and, consequently, applies a braking pressure force to said cable  50  against the fixed cam  1000 . Gravity feed is consequently slowed down by the braking pressure force on cable  50  between off center pivoting cam  1010  and fixed cam  1020 .  
         [0059]     This arrangement shown and described in connection with  FIGS. 13 and 14  has the benefit to easily control the speed of opening of the ladder sections  500 ,  600  and  700  and their fall to the ground. It can be used as a stand alone, or in combination with the devices that control the lowering down of the ladder to the ground.

Technology Category: 0