Abstract:
A ladder unit for climbing up and down a construction machine, capable of stabilizing a ladder in a position of descent thereof and that of storage thereof, facilitating an operator&#39;s actions to climb up and down the construction machine, and preventing the ladder from projecting toward circumferential parts and being thereby broken. Mechanisms for locking the ladder in the position of descent thereof are provided. The ladder locking force of these locking mechanisms is rendered releasable from the ladder in a position on the construction machine. Mechanisms for locking the ladder in its storage position are also provided.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a ladder unit for climbing up and down a construction machine, such as a large-sized hydraulic excavator.  
           [0003]    2. Description of the Related Art  
           [0004]    First, a related art hydraulic excavator will be described with reference to FIGS.  1 - 3  which show a mode of embodiment of the present invention as well. The hydraulic excavator is provided with a lower traveling unit  1 , an upper body  2  supported swingably on the lower traveling unit  1 , and a working machine  3  including a boom fixed pivotably to the upper body  2 , an arm and a bucket, and a cabin  4  is provided on the upper body  2 . When the hydraulic excavator is large-sized, a ladder unit A is used to be climbed up and down into and out of the operator&#39;s cabin  4 . This ladder unit A for climbing up and down the hydraulic excavator is fixed to the portion of a body frame  5  which is at a side portion of the upper body  2 .  
           [0005]    The related art ladder units for climbing up and down a construction machine include a ladder unit disclosed in, for example, Japanese Utility Model Laid-Open No. 4649/1985. This ladder unit for climbing up and down a construction machine will be described with reference to FIG. 4 which shows a mode of embodiment of the present invention as well. This ladder unit A is provided with a guide  10  fixed to the body frame  5 , and a ladder  11  supported slidably on this guide  10 . As shown in FIGS. 1 and 3, the guide  10  has a pair of, i.e. left and right guide members  12 ,  12  arranged in a mutually parallel condition. Each guide member  12  is provided with a ladder slider  13 , and a balance weight slider  14  formed on a rear portion of the ladder slider. The ladder  11  is provided slidably on the ladder sliders, and a balance weight  15  slidably on the balance weight sliders  14 . The ladder  11  and balance weight  15  are connected together by a rope  16 , an intermediate portion of which is passed around a sheave  17  supported rotatably via a shaft on top portions of the upper guides  12 .  
           [0006]    An operator on the ground pulls down the ladder  11  to a position of descent of the ladder as shown in FIG. 4B, climbs up onto a catwalk  6  of the upper body  2  by using this ladder, and then gets on the cabin  4  via a stairway  7 . The ladder is also used in a similar manner when, on the contrary, the operator climbs down from the upper body  2 .  
           [0007]    In the above-described related art ladder unit for climbing up and down a construction machine, the ladder  11  is always urged by the balance weight  15  so that the ladder is in a storage position thereof but the ladder is not in a locked state, in which a movement of the ladder is stopped, in the position of storage of the ladder and that of descent thereof. Therefore, even when the ladder  11  is pulled down to the position of descent thereof for the operator who is going to climb up the construction machine, the position of the ladder  11  is not stabilized, so that the operator&#39;s actions to climb up and down the construction machine cannot be made smoothly. The ladder  11  which ought to be in the position of storage thereof projects outward unexpectedly during an operation of the construction machine, and interferes with some other part to cause the ladder to be broken in some cases. Furthermore, since the related art ladder unit is fixed to the body frame with the ladder projecting outward from a side surface of the construction machine, the ladder interferes with some other part of the construction machine during an operation thereof, so that the ladder is liable to be broken.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention has been made in view of the above-mentioned circumstances, and provides a ladder unit for climbing up and down a construction machine, capable of stabilizing a ladder in a position of descent thereof to which the ladder is lowered, and facilitating an operator&#39;s actions to get on and off the ladder, and also a ladder unit for climbing up and down a construction machine, capable of preventing a ladder from projecting outward toward the surroundings and interfering with surrounding parts, and capable of solving a problem of the occurrence of breakage of the ladder ascribed to the outward projection of the ladder and the interference thereof with the mentioned parts.  
           [0009]    According to an aspect of the present invention, the ladder unit for climbing up and down a construction machine has a guide  10  provided on a body frame  5 , and a ladder  11  supported longitudinally slidably on the guide  10  and adapted to be moved up and down between a storage position in which the ladder is stored and a position of descent to which the ladder is lowered during the use thereof, the ladder unit being further provided with a locking mechanism  52  adapted to lock the ladder  11  in the position of descent thereof.  
           [0010]    In this ladder unit for climbing up and down a construction machine, a movement of the ladder  11  is stopped by the locking mechanism  52  in the position of descent to which the ladder is lowered. Therefore, the ladder  11  is stabilized in this position of descent, so that the operator&#39;s actions to get on and off the ladder can be made smoothly.  
           [0011]    According to another aspect of the present invention, the ladder unit for climbing up and down a construction machine has the locking mechanism  52  capable of releasing on the construction machine a ladder from a locking force of the locking mechanism.  
           [0012]    In this ladder unit for climbing up and down a construction machine, a locking operation of the locking mechanism  52  can be stopped, for example, from a position on a catwalk after an operator has climbed up to the catwalk. Therefore, an operation for storing the ladder  11  in a storage position can be carried out easily. For example, when the ladder  11  is adapted to be returned naturally to the storage position by using a balance weight  15 , the ladder  11  is restored as it is to the storage position by the above-mentioned ladder unlocking operation, whereby the degree of convenience of use of the ladder is improved.  
           [0013]    According to still another aspect of the present invention, the ladder unit for climbing up and down a construction machine has a locking mechanism  51  adapted to lock the ladder  11  in a storage position.  
           [0014]    In this ladder unit for climbing up and down a construction machine, the ladder  11  can be locked in a storage position as well, so that the unexpected projection of the ladder  11  during an operation of the construction machine can be prevented. This enables the inconvenience of occurrence of the breakage of the ladder, which is ascribed to the unexpected outward projection of the ladder  11  and the interference thereof with surrounding parts, to be eliminated.  
           [0015]    According to a further aspect of the present invention, the ladder unit for climbing up and down a construction machine has a balance weight  15  adapted to slide the ladder  11  to a storage position, and an urging device  41  adapted to urge the ladder  11  toward a position of descent thereof when the ladder  11  is locked in the storage position.  
           [0016]    In this ladder unit for climbing up and down a construction machine, the ladder  11  is moved forcibly toward the position of descent thereof by the urging device  41  when the ladder is unlocked in the storage position. This enables the unlocking of the ladder to be done reliably, and a later operation for pulling down the ladder  11  to be carried out easily and smoothly.  
           [0017]    According to another aspect of the present invention, the ladder unit for climbing up and down a construction machine has a detector  44  adapted to detect an unlocked condition of the ladder  11  in a position of storage thereof, and a device for stopping a movement of the construction machine when the ladder is released from a locking force.  
           [0018]    In this ladder unit for climbing up and down a construction machine, the stopping of a movement of the construction machine, for example, the stopping of the travel of a lower traveling unit  1  of a hydraulic excavator and a swinging movement of an upper body  2  thereof is carried out when the ladder  11  is not locked in the storage position. Accordingly, accidents, such as the breakage of the ladder unit can be prevented.  
           [0019]    According to still another aspect of the present invention, the ladder unit for climbing up and down a construction machine has a guide  10  provided on a body frame  5 , and a ladder  11  supported longitudinally slidably on the guide  10  and adapted to be moved up and down between a storage position in which the ladder is stored and a position of descent to which the ladder is lowered when the ladder is practically used, the ladder being provided so as not to project outward from a side surface of the construction machine when the ladder is in the storage position.  
           [0020]    In this ladder unit for climbing up and down a construction machine, the ladder  11  is provided so as not to project outward from a side surface of a construction machine when the ladder  11  is in a storage position. Therefore, the inconvenience of encountering the breakage of the ladder  11  in the case of a related art outwardly projecting ladder due to the interference of the same with surrounding parts can be eliminated. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    A preferred embodiment of the present invention will be described in detail with reference to the following figures, wherein:  
         [0022]    [0022]FIG. 1 is a front view of a hydraulic excavator as a mode of example of a construction machine provided with a ladder unit for climbing up and down the construction machine;  
         [0023]    [0023]FIG. 2 is a rear view of this hydraulic excavator;  
         [0024]    [0024]FIG. 3 is a plan view of the same hydraulic excavator;  
         [0025]    [0025]FIG. 4 illustrates a mode of embodiment of the ladder unit for climbing up and down a construction machine according to the present invention, wherein:  
         [0026]    [0026]FIG. 4( a ) is a sectional view of the mode of embodiment with a ladder in a storage position thereof; and  
         [0027]    [0027]FIG. 4( b ) is a sectional view of the mode of embodiment with the ladder in a position of descent thereof;  
         [0028]    [0028]FIG. 5 is an enlarged view showing a principal portion of a mechanism for locking the ladder in a position of storage thereof in the same mode of embodiment;  
         [0029]    [0029]FIG. 6 is an enlarged view showing a principal portion of a mechanism for locking the ladder in a position of descent thereof in the same mode of embodiment;  
         [0030]    [0030]FIG. 7 is an enlarged view of a principal portion showing a support structure for a locking rod in the same mode of embodiment;  
         [0031]    [0031]FIG. 8 is a sectional view showing a support structure for the ladder on a guide in the same mode of embodiment;  
         [0032]    [0032]FIG. 9 is a sectional view showing a support structure for a balance weight in the guide in the same mode of embodiment;  
         [0033]    [0033]FIG. 10 is a sectional view for describing an urging device provided on an upper portion of the guide in the same mode of embodiment; and  
         [0034]    [0034]FIG. 11 is an illustration for describing a detector provided on the guide and ladder in the same mode of embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0035]    A concrete mode of embodiment of the ladder unit for climbing up and down a construction machine according to the present invention will now be described in detail with reference to the drawings. FIG. 1 is a front view of a hydraulic excavator as a mode of example of a construction machine, FIG. 2 a rear view of the same hydraulic excavator, and FIG. 3 a plan view of the same.  
         [0036]    The hydraulic excavator in this mode of embodiment is provided with a lower traveling unit  1 , an upper body  2  supported swingably on the lower traveling unit  1 , and a working machine  3  including a boom fixed pivotably to the upper body  2 , an arm and a bucket, a cabin  4  being provided on the upper body  2 . At a side portion of the upper body  2 , a ladder unit A for climbing up and down a construction machine is fixed to the body frame  5 . This ladder unit A is utilized when an operator on the ground pulls down a ladder  11  to a position of descent thereof, climbs up the ladder onto a catwalk  6  of the upper body  2 , and gets on the cabin  4  via a stairway  7 . The ladder unit is also utilized similarly when the operator conversely climbs down the construction machine.  
         [0037]    The outline of the construction of the ladder unit A for climbing up and down a construction machine will be described on the basis of FIG. 4. This ladder unit A is provided with a guide  10  fixed to the body frame  2 , and the ladder  11  supported slidably on the guide  10 . FIG. 4A is a sectional view of the ladder  11  in a storage position in which the ladder is stored in the guide  10 , and FIG. 4B a sectional view of the ladder  11  in a position of descent thereof to which the ladder is drawn out. As shown in FIGS. 1 and 3, the guide  10  has left and right parallel-arranged guide members  12 ,  12 , and each of the guide members  12  extends diagonally downward at an angle of about  150  with respect to the body frame  2  as shown in FIG. 4. Each guide member  12  is provided with a ladder slider  13 , and a balance weight slider  14  formed in a position on the rear side of the ladder slider, and the ladder slider is slidably provided with ladder, and the balance weight slider is slidably provided with balance weight. The ladder slider  13  is opened sideways (refer to FIG. 8) so as to hold the slider  11  slidably. The ladder  11  and balance weight  15  are connected together by a rope  16 , an intermediate portion of which is passed around a sheave  17  supported via a shaft on a top portion of the guide member  12 . The weight of the balance weight  15  is set larger than that of the ladder  11 . Therefore, when an external force is not imparted at all to the ladder  11 , the ladder is drawn up by the balance weight  15 , and placed in the storage position shown in FIG. 4A. When the ladder  11  is put to use, it is pulled down.  
         [0038]    The structure of the ladder  11  will now be described. The ladder  11  is a step-connected device having left and right side members  18 ,  18  (only one of which is shown in FIG. 4), and footsteps  19  provided at predetermined intervals between the side members  18 ,  18 , and the side members  18 ,  18  are supported slidably in the ladder sliders  13  of the guide  10 . As shown in FIGS. 4 and 8, plural guide rollers  20  are provided on the side members  18 ,  18  so that the guide rollers  20  roll inside the ladder sliders  13 . Referring to FIG. 8, a reference numeral  21  denotes guide rails. As shown in FIG. 4, a ring type ladder-lowering handle  23  is fixed to a lower end portion of the ladder  11  via a chain  22 .  
         [0039]    The structure of the balance weight  15  will be described on the basis of FIG. 9. This balance weight  15  is provided with plural guide rollers  24 , which are adapted to roll on both upper and lower surfaces of the balance weight slider  14 . These guide rollers  24  are guided by rails  25  provided on both the upper and lower surfaces of the balance weight slider  14 .  
         [0040]    The characteristic point of the ladder unit for climbing up and down a construction machine resides in the provision of a locking mechanism for stopping a movement of the ladder  11  when the ladder  11  is in use and in a position of descent thereof and when the ladder is not in use and in a storage position. This locking mechanism has a locking rod  3 l supported retractably on a lower portion of the guide  10  of the body frame  5 , a stored ladder locking member  32  fixed to a lower portion of a rear surface of the ladder  11 , and a lowered ladder locking member  33  fixed to an upper portion of the rear surface of the ladder  11 . The locking rod  31  and stored ladder locking member  32  constitute a stored ladder locking mechanism  51 , and the locking rod  31  and lowered ladder locking member  33  a lowered ladder locking mechanism  52 .  
         [0041]    The details of a support structure for the locking rod  31  is shown in FIG. 7. As shown in the drawing, the locking rod  31  is supported slidably on a guide sleeve  34  fixed to the body frame  5 . The locking rod  31  is urged by a spring  35  as an urging device so that the locking rod projects toward the ladder  11 . In a position on a rear portion of the locking rod  31 , an arm  36  is supported pivotably on the body frame  5 , and this pivotable arm  36  is pin-connected to a rear end portion of the locking rod  31 . Namely, the locking rod  31  is set so that an urging force of the spring  35  enables the locking rod to be moved back away from the ladder  11  against the resilient force of the spring  35 . An operating handle  38  is fixed to the pivotable arm  36  via a chain  37 , so that the pivotable arm  36  can be turned by pulling down the operating handle  38 . Referring to FIG. 7, a reference numeral  39  denotes an operating knob. When a wire  40  joined to this operating knob  39  is connected to the pivotable arm  36  with the operating knob  39  then pulled up, the pivotable arm  36  can also be turned. This operating knob  39  is provided in a position in which the operator climbing up onto the catwalk  6  can operate the same.  
         [0042]    [0042]FIG. 7 shows the ladder  11  in a storage position, and the condition of the stored ladder locking mechanism  51  in this case is shown in FIG. 5. As shown in this drawing, the stored ladder locking member  32  provided on the rear surface of the ladder  11  moves up as it presses down the locking rod  31  during an upward movement of the ladder  11  toward the storage position. When the stored ladder locking mechanism which moves up gets beyond a position of the locking rod  31 , the locking rod  31  projects, and a lower end surface of the stored ladder locking member  32  engages the locking rod  31  from the upper side of the latter, whereby a downward movement of the ladder  11  is stopped. This stored ladder locking member  32  is tapered at the surface thereof by which the locking rod is pressed down, so as to enable an operation for pressing down the locking rod  31  while the stored ladder locking member  32  moves up and gets beyond the mentioned position to be carried out smoothly.  
         [0043]    [0043]FIG. 4B shows the ladder  11  in a lower position, and the condition of a lowered ladder locking mechanism  52  in this case is shown in FIG. 6. As shown in this drawing, the lowered ladder locking member  33  is set so that, when the lowered ladder locking member  33  provided on a rear surface of the ladder  11  moves down as it presses down the locking rod  31  while the ladder  11  moves down to a lower position, to get beyond a position of the locking rod  31 , the locking rod projects, and an upper end surface of the lowered ladder locking member  33  engages the locking rod  31  from the lower side of the latter to stop an upward movement of the ladder  11 . The lowered ladder locking member  33  is tapered at the surface thereof, by which the locking rod  31  is pressed down, more gently than the above-mentioned stored ladder locking member  32  so that an operation for pressing down the locking rod  31  can be carried out smoothly when the lowered ladder locking member  33  moves down as it presses down the locking rod  31 , to get beyond the position of the locking rod  31  as mentioned above. The operation of the stored ladder locking member  51  is carried out by the force of the balance weight, while the operation of the lowered ladder locking mechanism  52  is carried out by the operator&#39;s force against the force of the balance weight  15 . In view of this, the locking rod pressing surface of the lowered ladder locking member is tapered to reduce the force required for the operation of the lowered ladder locking mechanism  52 .  
         [0044]    Some other characteristic point of the ladder unit A will be described. This characteristic point resides in the use shown in FIG. 10 of a device, for example, a spring  41  for urging the ladder  11  downward when the ladder  11  is in the storage position shown in FIG. 4A. Namely, a bracket  42  is fixed to an upper portion of the guide  10 , and a pressure rod  43  is supported retractably on the bracket  42  and urged by the spring  41  in the direction in which the pressure rod projects outward. When the ladder  11  is in the storage position with the stored ladder locking member  32  engaged with the locking rod  31  as shown in FIG. 5, the pressure rod  43  is raised, and a pressing force works on the ladder  11  downward owing to the spring  41 . This structure is provided so as to lower the ladder  11  forcibly by a predetermined distance by the force of the spring  41  when the ladder is released from the locking force of the stored ladder locking mechanism  51 , and thereby reliably disengage the stored ladder locking member  32  and locking rod  31  from each other.  
         [0045]    Providing as shown in FIG. 11 a limit switch  44  as a device for detecting the condition of the ladder released from the locking force of the stored ladder locking mechanism  51  also constitute another characteristics of this mode of embodiment. Namely, the limit switch  44  is provided on the guide  10 , while a switch  45  for operating this limit switch  44  is fixed to the ladder  11 , so as to turn off the limit switch  44  when the ladder is locked by the stored ladder locking mechanism  51 , and turn on the limit switch  44  when the ladder is released from the locking force of the stored ladder locking mechanism. The on-off operations of the limit switch  44  are outputted to a controller (not shown). When the limit switch  44  is on, a movement of the lower traveling unit  1  and a swinging movement of the upper body  2  are prohibited, and the disengaged condition of the stored ladder locking mechanism  51  is displayed luminously on a panel inside the cabin  4 . Such a structure is provided so as to stop an operation of the construction machine by an operation stopping device (not shown) in the condition in which the locking force of the stored ladder locking mechanism  51  is released from the ladder, and thereby prevent an accident, such as the breakage of the ladder unit A.  
         [0046]    The operation of the ladder unit A for climbing up and down a construction machine will now be described. First, when the operator gets on the construction machine, the ladder unit A is in a stored state shown in FIGS. 4A and 7. The operator pulls down the operating handle  38 . Consequently, the pivotable arm  36  is turned, and the locking rod  31  is moved in the retracting direction against the force of the spring  35  to cause the ladder to be released from the locking force of the stored ladder locking mechanism  51 . During this time, the ladder  11  is pressed down by the urging force of the spring  41  shown in FIG. 10, and moved forcibly by a predetermined distance. This enables the locking force of the stored ladder locking mechanism  51  to be released reliably from the ladder. A ladder lowering handle  23  is then gripped with the mentioned parts left in the same condition, and pulled down. When the ladder  11  is lowered by a predetermined distance, a locking operation of the lowered ladder locking mechanism  52  is carried out automatically, so that the ladder  11  is locked in the position of descent to which the ladder is lowered. The operator then climbs up the ladder  11  onto the catwalk  6 .  
         [0047]    The operator on the catwalk  6  then pulls up the operating knob  39 . Consequently, the pivotable arm  36  is turned, and the locking rod  31  is moved in the retracting direction against the force of the spring  35  to cause the locking force of the lowered ladder locking mechanism  52  to be released from the ladder  11 . Consequently, the ladder  11  moves up automatically. After the ladder moves up by a predetermined distance, a locking operation of the stored ladder locking mechanism  51  is now carried out automatically, and the ladder  11  is locked in a ladder storage position. During this time, the spring  41  shown in FIG. 10 is compressed by an inertial force of the ascending ladder  11 . The operator then gets on the cabin  4  via the stairways  7 .  
         [0048]    When the operator gets off the construction machine, he takes a reverse procedure, i.e., he pulls up the operating knob  39  from a position on the catwalk  6  to release the locking force of the stored ladder locking mechanism  51  from the ladder. The lowered ladder locking mechanism  52  is locked automatically by the ladder lowering operation, and the operator then gets off the construction machine by utilizing the ladder  11 . The operator thereafter pulls down the operating handle  38  to release the locking force of the lowered ladder locking mechanism  52  from the ladder, and return the ladder automatically to the storage position by the force of the balance weight  15 , the ladder being then locked again by the stored ladder locking mechanism  51 .  
         [0049]    Since the ladder unit A is provided with the mechanism  51  for locking the ladder  11  in the lowered ladder locking position, the movement of the ladder  11  is stopped by the lowered ladder locking mechanism  52  in the position to which the ladder is pulled down. Therefore, the ladder  11  is stabilized in this position of descent thereof, so that the operator&#39;s actions to climb up and down the construction machine can be made smoothly.  
         [0050]    The operator can also release the locking force of the locking mechanism  52  from the ladder from a position on the catwalk  6 . This enables an operation for storing the ladder  11  in the storage position to be carried out easily. Namely, since the ladder  11  is set so as to be returned naturally to the storage position, the ladder  11  returns naturally as it is to the storage position by such an unlocking operation. Consequently, the degree of convenience of use of the ladder unit is improved.  
         [0051]    Since the mechanism  51  for locking the ladder  11  in the storage position is further provided so that the ladder  11  can be locked in the storage position as well, the occurrence of unexpected projection of the ladder  11  during an operation of the ladder unit can be prevented. This can prevent the ladder  11  from encountering its unexpected projection, and its interfering with a surrounding part to be broken.  
         [0052]    Since a spring is provided as a device  41  for urging when the ladder  11  is locked in the storage position thereof the ladder  11  toward a position of descent thereof, a forcible downward driving force occurs, when the ladder  11  is released from the locking force in the storage position thereof, in the ladder  11  due to the force of the urging device  41 , whereby the releasing of the locking force from the ladder can be done reliably. Accordingly, a subsequent ladder lowering operation can be carried out easily and smoothly. When such an urging device  41  is not provided, it is necessary to carry out a ladder lowering operation by gripping the ladder lowering handle  23  with the operating handle  38  in a pulled-down state. However, when the urging device  41  is provided, the ladder lowering operation can be carried out by gripping the ladder lowering handle  23  with the operator&#39;s hand released from the operating handle  38 .  
         [0053]    Furthermore, the ladder unit A is provided with the limit switch  44  for detecting a locking force-released condition of the ladder in the position in which the ladder  11  is stored, and a device for stopping an operation of the construction machine when the locking force is released from the ladder. Therefore, when the ladder  11  is not locked in the storage position, movement stopping operations, such as an operation for stopping the movement of the lower traveling unit  1  and an operation for stopping the swinging movement of the upper body  2  are carried out. This enables the occurrence of accidents, such as the breakage of the ladder unit A to be prevented.  
         [0054]    Still other characteristics of the mode of embodiment of the ladder unit A will now be described. The characteristics reside in the ladder  11  provided so that the ladder  11  does not project beyond a side surface of the construction machine when the ladder is in the storage position. Namely, as is clear from FIGS. 2 and 3, the ladder  11  and ladder unit A as a whole are arranged so that they do not project sideways when the ladder  11  is stored. As shown in the drawings, a part projecting sideways most of the hydraulic excavator in the mode of embodiment is the stairway  7 . The width of the hydraulic excavator is determined by the stairway  7 , and the ladder  11  and ladder unit A as a whole are arranged so that they do not project outward beyond the outer side surface of the stairway.  
         [0055]    Since the ladder  11  is provided so that the ladder in the storage position does not project beyond a side surface of the construction machine, the inconvenience of occurrence of the breakage of the ladder, which is ascribed to the interference of the ladder in a projecting state with the surrounding parts, can be eliminated.  
         [0056]    The above is a description of a concrete mode of embodiment of the present invention. The present invention is not limited to this mode of embodiment but can be practiced by modifying the invention in various ways within the scope thereof. For example, in the above-described mode of embodiment, the balance weight  15  is used to return the ladder  11  to the storage position. In order to move the ladder  11  to the storage position or a position of descent, some other driving power source, such as an electric motor, a hydraulic motor or a hydraulic cylinder may be used, and the present invention can also be applied to a ladder not having a driving power source. Although the ladder  11  in the storage position and stored entirely within the guide  10  is illustrated as an example, the stored condition of the ladder is not limited to only such a condition. The storage position referred to in this embodiment means a position in which the ladder is not in use.  
         [0057]    Although a hydraulic excavator is shown as a construction machine in the above-described mode of embodiment, the present invention can also be applied in completely the same manner to some other construction machine, such as a crawler crane.