Abstract:
To provide a crawler belt with no movable portion connected by pins etc., and to provide a crawler type traveling device with few rotating wheel mechanisms and equalizing the pressure contacting the ground. 
     A crawler type traveling device comprising: a driving wheel ( 12 ) driven by a driving axis ( 11 ); idler wheels ( 13 ) having axes parallel to that of the driving wheel; and a crawler belt which is spooled around the driving wheel and the idler wheels and travels around the driving wheel and the idler wheels. 
     The crawler belt comprising: an inner crawler belt ( 18 ) having an engaging structure engaging with the driving wheel, the inner crawler belt being driven by the driving wheel; an outer crawler belt ( 19 ) encircling circumferentially the outside of the inner crawler belt; a plurality of elastic members ( 20 ) connecting the inner crawler belt to the outer crawler belt; and a plurality of crawler plates ( 21 ) mounted to the outer crawler belt, and having lag for engaging with the ground.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a traveling device for a crawler type vehicle. More specifically, the present invention relates to a crawler type traveling device for a space robot and a space exploration vehicle, and a crawler type vehicle comprising such crawler type traveling devices. 
       BACKGROUND OF THE INVENTION 
       [0002]    The ground surfaces of a moon and planets are usually not stable ground. Instead, such ground surfaces are usually covered by sand, and thus have poor bearing power. Further, when a vehicle travels on the moon and planets on which the gravity is lower than that on earth, it is necessary to distribute the weight of the vehicle over a wide area, and to lower the pressure contacting the ground when traveling. 
         [0003]    One type of prior art space exploration vehicle has four to eight cylindrical wheels for enabling wide a ground area to be contacted. In such vehicle having wheels, the pressure contacting the ground is at a maximum under the wheels. Thus, the wheels are likely to be buried under the sand, and it would be difficult to continue traveling. 
         [0004]    One type of combat car or construction vehicle is a crawler type vehicle which comprises a driving wheel, idler wheels and a crawler belt spooled over the driving wheel and the idler wheel, and travels on the ground using the crawler belt. The crawler type vehicle contacts a wide area of ground, and thus has a good traveling capability even on a soft ground. 
         [0005]    The crawler type traveling device comprises a crawler belt having a plurality of crawler plates made of a rigid metal, the crawler plates being pivotally connected to adjacent plates by pins. The crawler belt goes around the driving wheel and the idler wheels. Another crawler belt is made of a rubber having flexibility, and does not have crawler plates connected by pins. 
         [0006]    Under a vacuum or low pressure atmosphere on the moon or planets, pin portions which connect the crawler plates have poor lubricity, and thus have much friction. Thus, durability is degraded. 
         [0007]    The crawler belt made of rubber exhausts much gas out of the belt and is easily degraded, and thus it is not suitable to use in space. 
         [0008]    Further, a crawler type vehicle needs a lot of rotating wheel mechanisms for equalizing the pressure contacting the ground. Thus this mechanism is complicated and heavy, and reliability is degraded thereby. 
         [0009]    Patent Document 1 (JP 2005-111595) discloses a crawler type traveling robot comprising a base, a crawler provided on each of the right and left sides of the base, and an arm provided on the base. Each crawler comprises a driving wheel provided at one end thereof in a longitudinal direction, a traveling motor for driving the driving wheel, an idling wheel provided at the other end thereof in a longitudinal direction, an endless track engaging the driving wheel and idling wheel and spooled around both wheels, a center wheel engaging the endless track at the center portion of the crawler and a central motor for driving the center wheel. 
         [0010]    However, the crawler type traveling robot shown in patent document 1 does not contact the ground with uniform pressure. Further, there is a possibility that stones or sand will easily enter into the engaging portions of the crawler belt and the driving wheel. 
         [0011]    Patent Document 1: JP 2005-111595 
       SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
       [0012]    An object of the present invention is to provide a crawler belt with no movable portion connected by pins etc., and thus to provide a crawler type traveling device which has no lubricating problem. 
         [0013]    An object of the present invention is to provide a crawler type traveling device with few rotating wheel mechanisms which equalizes the pressure thereof contacting the ground. 
         [0014]    Another object of the present invention is to provide a crawler type traveling device in which stones or sand will not easily enter into the engaging portions of the crawler belt and the driving wheel. 
         [0015]    A further object of the present invention is to provide a crawler type vehicle having such crawler type traveling devices. 
       Means to solve the Problem 
       [0016]    In the present invention, a crawler belt (assembly) comprises a double crawlers configuration having an outer crawler belt and an inner crawler belt. Each of the outer and inner crawler belts is made of a thin metal plate or resin plate having a ring shape and flexibility. The outer crawler belt and the inner crawler belt are connected by elastic members. The elastic members are deformable so that the outer crawler belt and the inner crawler belt can come near to each other and far away. Thus the outer crawler is deformable according to the conditions of the ground, and thus the ground is contacted with uniform pressure. 
         [0017]    One aspect of the present invention is a crawler type traveling device comprising: 
         [0018]    a driving wheel driven by a driving axis; 
         [0019]    idler wheels having axes parallel to that of the driving wheel; and 
         [0020]    a crawler belt which is spooled around the driving wheel and the idler wheels and travels around the driving wheel and the idler wheels; 
         [0021]    wherein the crawler belt comprises: 
         [0022]    an inner crawler belt having an engaging structure engaging with the driving wheel, the inner crawler belt being driven by the driving wheel; 
         [0023]    an outer crawler belt encircling circumferentially the outside of the inner crawler belt; 
         [0024]    a plurality of elastic members connecting the inner crawler belt and the outer crawler belt along the circumferential direction of the crawler belt; and 
         [0025]    a plurality of crawler plates mounted to the outer crawler belt, and having lag (lag constitution) for engaging with the ground. 
         [0026]    The crawler belt comprises a double crawler belts configuration including an outer crawler belt and an inner crawler belt, and the inner crawler belt engages with the driving wheel. Thus, the inner crawler belt is not likely to contact the ground surface, and thus stones or sand will not easily enter into the engaging portions between the crawler belt and the driving wheel. 
         [0027]    The crawler belt itself has flexibility in the thickness direction thereof due to the elastic members. The outer crawler belt is deformable according to the shape of the ground and stones. Thus, the ground is contacted with uniform pressure and a high driving force is obtained. 
         [0028]    Preferably, the inner crawler belt and the outer crawler belt are each made of a thin metal plate or resin plate having a ring shape and flexibility. 
         [0029]    The crawler belt does not have a movable portion connected by a pin etc., and thus there is no lubricating problem. 
         [0030]    Preferably, the elastic members connecting the inner crawler belt and the outer crawler belt are made of an elastic metal plate having a curved shape. 
         [0031]    Because the crawler belt is made of metal, there is no gas exhausted out of the belt, and thus it is suitable for use in space. 
         [0032]    Preferably, one end of each of the elastic members may be connected to the end in the width direction of the inner crawler belt, the other end of each of the elastic members is connected to the end in the width direction of the outer crawler belt, and the intermediate portion of each of the elastic members has a concaved shape bent toward the center portion in the width direction of the crawler belt. 
         [0033]    Thus the crawler belt having good elasticity is obtained. 
         [0034]    Preferably, the driving wheel has protrusions at regular intervals at its center portion in the width direction thereof, the inner crawler belt has recesses which engage with the protrusions at its center portion in the width direction thereof, and the driving wheel drives the inner crawler belt. 
         [0035]    The protrusions and the recesses comprise an engaging structure. 
         [0036]    Preferably, the driving wheel has protrusions at regular intervals at the ends in the width direction thereof, the inner crawler belt has recesses which engage with the protrusions at the ends in the width direction thereof, and the protrusions engage the recesses, and the driving wheel drives the inner crawler belt. 
         [0037]    The crawler belt is thus driven more reliably. 
         [0038]    Preferably, the outer crawler belt comprises a wire crawler belt made of a plurality of metal wires extending in the circumferential direction of the outer crawler belt, and a plurality of the crawler plates are connected to the wire crawler belt at regular intervals. 
         [0039]    The wire crawler belt is more deformable, and thus more conformable to the shape of the ground surface. 
         [0040]    Preferably, the outer crawler belt comprises a mesh crawler belt made of a metal mesh having wires extending in the circumferential direction and in the width direction of the outer crawler belt, and a plurality of the crawler plates are connected to the wire crawler belt at regular intervals. 
         [0041]    The mesh crawler belt has a more stable performance than the wire crawler belt. 
         [0042]    The crawler type traveling device may further comprises a side cover covering the sides of the driving wheel, the idle wheels and the inner crawler belt, the end of the side cover extending to the portion between the inner crawler belt and the outer crawler belt. 
         [0043]    Stone and sand are thus prohibited from entering the engaging portions of the crawler type traveling device. 
         [0044]    The crawler type traveling device may further comprise rotating wheels having axes parallel to that of the driving wheel; and the crawler belt which is spooled around the driving wheel, the idler wheels and the rotating wheels, and travels around the driving wheel, the idler wheels and the contact wheels. 
         [0045]    Because there are a number of the wheels engaging the crawler belt, the ground surface is contacted with a more uniform pressure. 
         [0046]    Another aspect of the present invention is a crawler type vehicle including crawler type traveling devices, each of the crawler type traveling device comprising: 
         [0047]    a driving wheel driven by a driving axis; 
         [0048]    idler wheels having axes parallel to that of the driving wheel; and 
         [0049]    a crawler belt which is spooled around the driving wheel and the idler wheels and travels around the driving wheel and the idler wheels; 
         [0050]    wherein the crawler belt comprises: 
         [0051]    an inner crawler belt having a engaging structure engaging with the driving wheel, the inner crawler belt being driven by the driving wheel; 
         [0052]    an outer crawler belt encircling circumferentially the outside of the inner crawler belt; 
         [0053]    a plurality of elastic members connecting the inner crawler belt and the outer crawler belt along the circumferential direction of the crawler belt; and 
         [0054]    a plurality of crawler plates mounted to the outer crawler belt, and having lag for engaging with the ground. 
       Advantageous Effect of the Invention 
       [0055]    In the present invention, the crawler belt comprises a double crawler belts configuration having an outer crawler belt and an inner crawler belt. The outer crawler belt contacts the ground surface, and the inner crawler belt engages to the driving wheel. Thus, the inner crawler belt is not likely to contact the ground surface, and thus stones or sand will not easily enter into the engaging portions of the inner crawler belt and the driving wheel. 
         [0056]    The crawler belt itself has flexibility in the thickness direction thereof. Thus, the outer crawler belt is deformable according to the shape of the ground and stones. Thus, the pressure with which the ground is contacted can be low, and a high driving force is obtained. Thus, the crawler type device is not likely to be buried in the sand, and has a good traveling capability. 
         [0057]    The crawler belt itself has flexibility due to the elastic members and pushes the outer crawler belt to the ground. Thus the number of the rotating wheels which push the crawler to the ground can be reduced. Therefore, the structure of the crawler type travelling device can be simplified, the weight can be reduced, and thus increased reliability can be obtained. 
         [0058]    Further, the elastic members connecting the inner crawling wheel and the outer crawling wheel have a shape bending inwardly, and thus the side surface of the elastic members would not cause the ground to collapse. 
         [0059]    Further, since the rotating wheels do not easily contact the ground or stones, the diameter of the rib of the rotating wheels for preventing the crawler belt from deviating is not limited to a small diameter. 
         [0060]    According to the present invention, a crawler belt with no movable portions connected by pins etc. is provided, and thus a crawler type traveling device having no lubricating problem is provided. 
         [0061]    A crawler type traveling device is provided having a small number of rotary mechanisms, and the ground is contacted with uniform pressure. 
         [0062]    Further, a crawler type vehicle is provided having such crawler type traveling devices. 
       DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0063]    Now, embodiments of the present invention will be described. The embodiments relate to a crawler type traveling device for a space robot and a space exploration vehicle. However, the present invention is not limited to the crawler type vehicle for use in space. That is, the present invention can be used for crawler type vehicles for various household applications. 
         [0064]      FIG. 1(A)  shows a schematic side view of a crawler unit  10  of a crawler type traveling device according to a first embodiment of the present invention, and  FIG. 1(B)  shows a front view thereof. In the description of the present invention, one crawler unit  10  is referred to as a crawler type traveling device. 
         [0065]    The crawler unit  10  (crawler type traveling device) comprises a rotating driving axis  11  connected to an actuator (a driving source, not shown) such as a motor, and a cylindrical sprocket (a driving wheel)  12 . Protrusions  12   a  are provided for engaging to a crawler wheel around the sprocket  12 . Ribs which have a large diameter (flange)  12   c  are provided at the ends in the width direction of the sprocket  12  for holding the crawler belt. 
         [0066]    In the prior art crawler mechanism, if the diameter of the ribs is too large, the ribs protrude out of the crawler belt, and thus the ribs are likely to contact the ground directly. Thus, the diameter of the ribs can not be too large. The crawler belt of the present invention has double crawler belts and is thick, and thus the diameter of the ribs can be large. 
         [0067]    The crawler unit  10  also comprises a front idler wheel  13   a  which has a cylindrical shape and a rear idler wheel  13   b  which has a cylindrical shape. The axis of the front idler wheel  13   a  and the axis of the rear idler wheel  13   b  are parallel to the axis of the sprocket  12 . Ribs  13   c  which have a large diameter are provided at the ends in the width direction of the idler wheels  13   a,    13   b  for holding the crawler belt. 
         [0068]    The crawler unit  10  comprises a holding member  17  for holding each member of the crawler unit  10 , the holding member  17  being the main structure of the crawler unit  10 . The sprocket  12 , the front idler wheel  13   a,  the rear idler wheel  13   b  and other members are mounted to the holding member  17 . 
         [0069]    A crawler belt is spooled around the sprocket  12 , the front idler wheel  13   a  and the rear idler wheel  13   b.  The crawler belt includes an inner crawler belt  18  for engaging the sprocket  12 , the front idler wheel  13   a  and the rear idler wheel  13   b.  The inner crawler belt  18  is made of a metal plate or a resin plate having a thin ring shape (short cylindrical shape), and is flexible, and thus can go around the sprocket  12  and the idler wheels  13   a,b  by following the outer shapes of the sprocket  12  and the idler wheels  13   a,b.  The inner crawler belt  18  has holes for engaging the protrusions  12   a  of the sprocket  12 . The protrusions  12   a  of the sprocket  12  engage the holes of the inner crawler belt  18  to drive the inner crawler belt  18 . 
         [0070]    The crawler unit  10  comprises an outer crawler belt  19  encircling circumferentially the inner crawler belt  18 . The outer crawler belt  19  is made of a metal plate or a resin plate having a thin ring shape, and is flexible. The outer crawler belt  19  has a wider width than that of the inner crawler belt  18 . Alternatively, the outer crawler belt  19  may have substantially the same width as that of the inner crawler belt  18 . 
         [0071]    The inner crawler belt  18  is connected to the outer crawler belt  19  by elastic members  20 . One end of each of the elastic members  20  is connected to an end in the width direction of the inner crawler belt  18 , and the other end of each of the elastic members  20  is connected to an end in the width direction of the outer crawler belt  19 . Each of the intermediate portions of the elastic members  20  is bent toward the center portion in the width direction of the crawler belt. The elastic members  20  are made of elastic metal, and thus are easily deformable in the thickness direction of the crawler belt. 
         [0072]    The crawler belt is integrally comprised of the inner crawler belt  18 , the outer crawler belt  19  and the elastic members  20 . The crawler belt has flexibility, and can go around the sprocket  12  and the idler wheels  13   a,    13   b.    
         [0073]    Crawler plates  21  are provided around the outer crawler belt  19 . The structures of the crawler plates  21  will be explained later referring to  FIGS. 4 and 5 . 
         [0074]    Further, the crawler unit  10  comprises a tensioner  14 . The tensioner  14  presses the inner crawler belt  18  from the inside so that the inner crawler belt  18  will not bend inwardly. 
         [0075]    Further, the crawler unit  10  comprises a brush  15 . The brush  15  engages the inner crawler belt  18  from the inside to brush out the stones and sand adhered to the inner crawler belt  18 . 
         [0076]    Further, the crawler unit  10  comprises a side cover  16 . (In  FIG. 1(A) , the side cover  16  is shown in dashed lines so that inner members can be seen.) The side cover  16  covers the sides of the sprocket  12 , the front idle wheel  13   a,  the rear idle wheel  13   b  and the inner crawler belt  18  to preventing stones and sand entering into the engaging portions of the inner crawler belt and the sprocket. The shape of the side cover  16  will be explained referring to  FIG. 8  later. 
         [0077]      FIG. 2  is a schematic view of a crawler type vehicle having a pair of the crawler units  10  at the right and left sides of the car body  30 . 
         [0078]      FIG. 3  is a schematic side view of a crawler type vehicle having a pair of the crawler units  10  connected to a steering mechanism at a front portion of the car body  30  and a pair of the crawler units  10  at a rear portion of the car body  30 . A pivot hinge  34  is provided at the center portion in the longitudinal direction of the car body  30 , the pivot hinge  34  extending in the transverse direction of the car body  30 . Pivot beams  33  are mounted to the pivot hinge  34 , the pivot beams  33  being substantially parallel to the sides of the car body  30 . The pivot beams  33  can be pivoted around the pivot hinge  34 . While the crawler type vehicle is traveling, when the front crawler unit  10  has a height different from that of the rear front crawler unit  10 , the crawler type vehicle can follow the shape of the ground. 
         [0079]    Steering mechanisms  32  are provided at both ends of each of two pivot beams  33 . The steering mechanism  32  can rotate the crawler unit  10  around the axis in the vertical direction to turn the crawler unit  10 . Instead, the steering mechanism  32  can be provided at only one end of each of the two pivot beams  33 . 
         [0080]      FIG. 4(A)  shows a schematic plane view of a portion of the crawler belt, and  FIG. 4(B)  is a cross sectional view along A-A line of  FIG. 4(A) . 
         [0081]    The outer crawler belt  19  encircles the inner crawler belt  18  which has a short cylindrical shape. The inner crawler belt  18  is connected to the outer crawler belt  19  by a plurality of the elastic members  20 . All around the inner crawler belt  18 , the elastic members  20  are provided at regular intervals in the longitudinal direction of the inner crawler belt  18 . Each of the elastic members  20  connects one end in the width direction of the inner crawler belt  18  to one end in the width direction of the outer crawler belt  19 . Each of the intermediate portions of the elastic members  20  between the inner crawler belt  18  and the outer crawler belt  19  is bent toward the center portion in the width direction of the crawler belt. That is, the elastic members  20  has a curved shape. 
         [0082]    The elastic members  20  are made of metal such as a stainless steel having a thin thickness, and thus can be easily deformable. Thus the interval between the inner crawler belt  18  and the outer crawler belt  19  can be easily changed according to the shape of the ground, the outer crawler belt  19  following the shape of the ground. 
         [0083]    The elastic members  20  may have other shapes than that shown here so long as they are easily deformable. For example, each of the elastic members  20  may not be parallel to the width direction of the inner crawler belt  18 , but instead may be oblique to the width direction of the inner crawler belt  18 . 
         [0084]    Crawler plates  21  are provided around the outer crawler belt  19  at regular intervals in the circumferential direction. The crawler plates  21  are made of a rigid metal. The crawler plates  21  engage the ground to obtain driving strength. 
         [0085]    The elastic members  20 , the outer crawler belt  19  and the crawler plates  21  are connected to each other by bolts  25 . Each of the crawler plates  21  is mounted to the outer crawler belt  19 , the crawler plates  21  not being connected to each other by pins. 
         [0086]      FIG. 5  is a perspective view of the crawler plates  21  provided around the outer crawler belt  19 . The crawler plates  21  have substantially the same width as that of the outer crawler belt  19 . Lags  21   a  extend in the vertical direction from one end of each of the base portions of the crawler plates  21  which are adjacent to the outer crawler belt  19 . The lags  21   a  have substantially the same width as that of the crawler plates  21 . The lags  21   a  have substantially the same height. The lags  21   a  are for definitely engaging the crawler plates  21  with the ground, and thus the shape of the lags  21   a  is not limited as long as the lags  21   a  engage with the ground. The crawler plates  21  have recesses  21   b  at their respective base portions. The recesses  21   b  are for preventing the crawler plates  21  from slipping. The recesses  21   b  may have any shape as long as the crawler plates  21  are prevented from slipping. The recesses  21   b  are optional. 
         [0087]    The crawler plates  21  have protrusions  21   c.  The protrusions  21   c  prevent the crawler plates  21  from slipping. The protrusions  21   c  have female screws (not shown) on their respective undersides so that the crawler plates  21  can be connected to the outer crawler belt  19  by the bolts  25 . The protrusions  21   c  are optional. 
         [0088]    The outer crawler belt  19  may have sand holes  19   b.    
         [0089]      FIG. 6(A)  is a plane view showing the engagement (engaging structure) between the sprocket  12  and the inner crawler belt  18  of a second embodiment of the present invention, and  FIG. 6(B)  is a cross sectional view along A-A line of  FIG. 6(A) . FIG.  6 (A)(B) is for showing the engagement between the sprocket  12  and the inner crawler belt  18 , and thus the members such as the outer crawler belt  19  and the elastic members  20  are not shown. In the second embodiment, the inner crawler belt  18  engages the sprocket  12  not only at the center portion in the width direction of the inner crawler belt  18 , but also at both ends of the inner crawler belt  18 . 
         [0090]    The sprocket  12  has protrusions  12   a  at regular intervals at the center portion in the width direction of the inner crawler belt  18 . The inner crawler belt  18  has holes  18   b  for inserting the protrusions  12   a  of the sprocket  12  at the same intervals as those for the protrusions  12   a.  The protrusions  12   a  of the sprocket  12  engage with the holes  18   b  of the inner crawler belt  18  to drive the inner crawler belt  18 . 
         [0091]    In the second embodiment, the sprocket  12  does not have the ribs  12   c  of the same height, but instead has protrusions  12   b  at regular intervals at both ends in the width direction around the sprocket  12 . The inner crawler belt  18  has recesses  18   c  for inserting the protrusions  12   b  of the sprocket  12  at the same intervals as those for the protrusions  12   b.  The protrusions  12   a  of the sprocket  12  engage the holes  18   c  of the inner crawler belt  18  to drive the inner crawler belt  18 . The protrusions  12   b  of the sprocket  12  also hold the inner crawler belt  18  so that the inner crawler belt  18  will not deviate from the sprocket  12 . 
         [0092]      FIG. 7  is a perspective view showing a portion of the crawler belt of a second embodiment. The inner crawler belt  18  has recesses  18   c  at both ends in the width direction of the inner crawler belt  18 . In  FIG. 7 , the inner crawler belt  18  has two rows of holes  18   b.  The elastic members  20  are connected to the outer crawler belt  19  by bolts  25 . 
         [0093]      FIG. 8(A)  is a side view of the crawler unit of the second embodiment showing that the side cover  16  covers the ends of the sprocket  12  and the idler wheels  13   a,   13   b,  and  FIG. 8(B)  is a schematic cross sectional view. A brush  15  is shown in  FIG. 8(A) . The first embodiment has the same side cover  16  as that in the second embodiment. The side cover  16  is mounted to the holding member  17 , and covers the ends of the sprocket  12  and the idler wheels  13   a,   13   b.  The end  16   a  of the side cover  16  extends to the recessed portions of the elastic members  20  between the inner crawler belt  18  and the outer crawler belt  19 . This structure prevent stones and sand from entering into the engaging portions of the inner crawler belt  18  and the sprocket  12 . 
         [0094]    As shown in the schematic cross sectional view of  FIG. 8(B) , the protrusions  12   b  of the sprocket  12  engage the recesses of the inner crawler belt  18 . The idler wheels  13   a,b  have ribs  13   c  at both ends in the width direction of the idler wheels. The ribs  13   c  hold both ends of the inner crawler belt  18  so that the inner crawler belt  18  will not deviate from the idler wheels  13   a,b.    
         [0095]      FIG. 9(A)  is a schematic perspective view of a portion of the crawler unit of a third embodiment showing a wire crawler belt  23  which is the outer crawler belt. The outer crawler belt has a plurality of wires parallel to the longitudinal direction of the outer crawler belt. Crawler plates  21  are mounted to the wire crawler belt  23  at regular intervals. 
         [0096]    The wire crawler belt  23  is more deformable than the outer crawler belt  19  of the embodiment shown in  FIG. 1 , and thus more conformable to the shape of the ground surface. 
         [0097]      FIG. 9(B)  is a schematic perspective view showing a portion of a mesh crawler belt  24 . 
         [0000]    The mesh crawler belt  24 , in addition to the wires shown in  FIG. 9(A) , has wires orthogonal to the wires shown in  FIG. 9(A) . The mesh crawler belt  24  has wires in the longitudinal direction and width direction thereof, and thus a stable performance is obtained. 
         [0098]      FIG. 10(A)  is a schematic side view of a fourth embodiment of the present invention showing a crawler unit  10 ′, and  FIG. 10(B)  is a front view thereof. The crawler unit  10 ′ is different from the crawler unit  10  of the first embodiment shown in  FIG. 1  in that the crawler unit  10 ′ has rotating wheels  22   a,    22   b  in addition to the idler wheels  13   a,    13   b.  The other members of the crawler unit  10 ′ are the same as those of the crawler unit  10  shown in  FIG. 1 . That is, the ribs  12   c  which have the same height are provided at the ends in the width direction of the sprocket  12 . Because the crawler unit  10 ′ has a lot of wheels which engage the crawler belt, the ground is contacted with more uniform pressure. 
       EXAMPLES  
       [0099]      FIG. 11  is a perspective view of an example of the crawler unit  10  of the first embodiment shown in  FIG. 1 . The ribs  12   c  which have the same height are provided at the ends in the width direction around the sprocket  12 . There are no protrusions  12   b  of the second embodiment shown in  FIG. 6 . The cover  16  is not provided in this example. 
         [0100]      FIG. 12  is a photograph of an example of the crawler unit  10  of the first embodiment shown in  FIG. 1 . This example has the sprocket and the idler wheels made of aluminum alloy (a diameter of about 140 mm and thickness of about 3 mm), the inner crawler belt  18  and the outer crawler belt  19  made of stainless steel (a thickness of 0.2 mm and width of 65 mm), the elastic members  20  made of stainless steel (a thickness of 0.2 mm and width of 10 mm) and the crawler plates made of aluminum alloy (10×10×1.5 mm aluminum angle bar). The example shown in  FIG. 12  has the elastic members  20  which are not orthogonal to the direction of the crawler belt but instead oblique to it. 
       INDUSTRIAL APPLICABILITY  
       [0101]    The crawler type vehicle having the crawler type traveling devices of the present invention contacts the ground with a uniform pressure, and has a simple structure suitable for use in space. The present invention can also be used as a crawler type vehicle for households. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0102]      FIG. 1(A)  shows a schematic side view of a crawler unit  10  of a crawler type traveling device according to the first embodiment of the present invention (the cover is shown in dashed lines), and  FIG. 1(B)  shows a front view thereof. 
           [0103]      FIG. 2  is a schematic view of a crawler type vehicle having a pair of the crawler units at right and left sides of the body of the vehicle. 
           [0104]      FIG. 3  is a schematic side view of a crawler type vehicle having a pair of the crawler units connected to the steering mechanism at the front portion of the car body and a pair of the crawler units at the rear portion of the car body. 
           [0105]      FIG. 4(A)  is a schematic plane view of a portion of the crawler belt,  FIG. 4(B)  is a cross sectional view along A-A line of  FIG. 4(A) . 
           [0106]      FIG. 5  is a perspective view of the crawler plates provided around the outer crawler belt. 
           [0107]      FIG. 6(A)  is a plane view showing the engagement between the sprocket and the inner crawler belt of the second embodiment, and  FIG. 6(B)  is a cross sectional view along A-A line of (A). 
           [0108]      FIG. 7  is a perspective view showing a portion of the crawler belt of the second embodiment. 
           [0109]      FIG. 8(A)  is a schematic side view showing the side cover, and  FIG. 8(B)  is a schematic cross sectional view of the second embodiment. 
           [0110]      FIG. 9(A)  is a schematic perspective view showing a portion of the wire crawler belt (the outer crawler belt) of the third embodiment, and  FIG. 9(B)  is a schematic perspective view of a portion of the mesh crawler belt. 
           [0111]      FIG. 10(A)  is a schematic side view showing a crawler unit of the fourth embodiment of the present invention, and  FIG. 10(B)  is a front view. 
           [0112]      FIG. 11  is a perspective view of the example of the crawler unit of the first embodiment shown in  FIG. 1 . 
           [0113]      FIG. 12  is a photograph of the example of the crawler unit of the first embodiment shown in  FIG. 1 . 
       
    
    
     EXPLANATION OF REFERENCE NUMERALS  
       [0114]      10  crawler unit 
         [0115]      11  rotating driving axis 
         [0116]      12  sprocket (driving wheel) 
         [0117]      12   a, b  protrusion 
         [0118]      12   c  rib 
         [0119]      13   a  front idler wheel 
         [0120]      13   b  rear idler wheel 
         [0121]      13   c  rib 
         [0122]      14  tensioner 
         [0123]      15  brush 
         [0124]      16  side cover 
         [0125]      17  holding member 
         [0126]      18  inner crawler belt 
         [0127]      18   b  hole 
         [0128]      18   c  recess 
         [0129]      19  outer crawler belt 
         [0130]      19   b  sand hole 
         [0131]      20  elastic member 
         [0132]      21  crawler plate 
         [0133]      21   a  lag 
         [0134]      21   b  recess 
         [0135]      21   c  protrusion 
         [0136]      22  rotating wheel 
         [0137]      23  wire crawler belt 
         [0138]      24  mesh crawler belt 
         [0139]      25  bolt 
         [0140]      30  car body 
         [0141]      31  traveling device 
         [0142]      32  steering mechanism 
         [0143]      33  pivot beams 
         [0144]      34  pivot hinge 
         [0145]      35  car body