Patent Publication Number: US-2021178953-A1

Title: Transport vehicle

Description:
TECHNICAL FIELD 
     This disclosure relates to a transport vehicle, especially to a transport vehicle having a lifter. 
     BACKGROUND 
     Conventionally, a transport vehicle having a lifter has been known (refer to WO 2013/001906 A1, for example). WO &#39;906 discloses a fork lift 2, for example. The fork lift 2 includes a pair of right and left side frames 4, 6, and a rear frame 8. 
     A conventional transport vehicle with a lifter can transport a heavy article (about 1000 kg, for example) while lifting up the article. It is necessary to reinforce the main frame to deal with the heavy load, but the reinforcement of the main frame enlarges the body. Body enlargement increases the whole weight of the transport vehicle so that it is necessary to enlarge the batteries and the motors as well. 
     In addition, since a conventional transport vehicle with a lifter includes a main frame and a frame for a lifter as different members, the doubled frames cause a useless space for ensuring attachment portions. 
     It could therefore be helpful to provide a way to downsize a transport vehicle with a lifter. 
     SUMMARY 
     We thus provide: 
     A transport vehicle includes a pair of right and left vehicle body frames, driving wheels, auxiliary wheels, and lifter mechanisms. 
     The pair of left and right vehicle body frames extends in a front and back direction. 
     Each of the driving wheels are disposed at a middle portion in the front and back direction of the pair of left and right vehicle body frames. The total number of the driving wheels is two. 
     Each of the auxiliary wheels are disposed at a lower portion of an end portion in the front and back direction of each of the right and left vehicle body frames. The total number of the auxiliary wheels is four. 
     Each of the lifter mechanisms are disposed at an upper portion of an end portion in the front and back direction of each of the right and left vehicle body frames. The total number of the lifter mechanisms is four. 
     According to the transport vehicle, portions on which the lifter mechanisms are placed are the frame, which supports the driving wheels and the auxiliary wheels. Accordingly, it is possible to integrate the lifter mechanisms with the frame, thereby manufacturing the transport vehicle attaining downsizing and light weighting. 
     In addition, according to the transport vehicle, since the lifter mechanisms and the auxiliary wheels are provided at the end portions in the front and back direction of each of the vehicle body frames, the lifter mechanisms are disposed in the vicinity of the auxiliary wheels. Accordingly, the heavy load is unlikely to be applied to a portion of the frame other than ends thereof, thereby manufacturing the transport vehicle attaining downsizing and light weighting. 
     The locations of the auxiliary wheels and the lifter mechanisms may correspond to each other or may be different form each other in planar view. 
     The transport vehicle may further include a connection frame and a lower frame. 
     The connection frame connects upper portions of the pair of right and left vehicle body frames with each other. 
     The lower frame may be able to be disposed between the pair of right and left vehicle body frames. The lower frame may be removably fixed at lower portions of the pair of right and left vehicle body frames. 
     According to the transport vehicle, since the vehicle body frame and the lower frame constitute a dividing structure, it is easy to access components installed inside of the transport vehicle. 
     The connection frame may connect middle portions in the front and back direction of the pair of right and left vehicle body frames with each other. 
     According to the transport vehicle, which has a frame with a simple structure, enough strength is obtained. Especially, when the transport vehicle travels over a rough surface of the floor and a large force is partially applied, the stress is distributed because the pair of right and left vehicle body frames are connected with each other only at the middle portions in the front and back direction so that the whole body is likely to bend. 
     Each of the lifter mechanisms may include an elevating motor, an elevating transmission shaft, and a bearing. 
     The elevating motor may be disposed at an upper portion of each of the right and left vehicle body frames or the connection frame. 
     The elevating transmission shaft is elevated by driving of the elevating motor. 
     The bearing supports the elevating transmission shaft such that the elevating transmission shaft can move in the vertical direction. 
     According to the transport vehicle, the elevating motor is supported by the vehicle body frame or the connection frame too, thereby making smaller the transport vehicle. 
     The transport vehicle may further include an electrical component disposed at an upper face of the lower frame. The electrical component may be located at a position different from that of the connection frame in planar view. 
     According to the transport vehicle, since the electrical component is disposed at a position different from that of the connection frame in planar view, it is possible to arrange at least parts of the electrical components and the connection frame at the same level, thereby making it possible to make the transport vehicle compact in the height direction. 
     The lower frame may be able to be removed below to leave as one member by itself from the pair of right and left vehicle body frames. 
     According to the transport vehicle, since the vehicle body frame and the lower frame constitute a dividing structure, it is possible to detach the lower frame and the electrical component below from the vehicle body frame with one action. In other words, maintainability is improved. In addition, when the assembly work is performed, it is possible to perform a process for the vehicle body frame and a process for the lower frame in parallel, thereby shortening the manufacturing time. 
     Each of the vehicle body frames may include a main portion that carries the lifter mechanisms, and a reinforcement portion extending below from the main body. 
     According to the transport vehicle, since the vehicle body frame has the reinforcement portion, strength is improved while maintaining a light weight. 
     Our transport vehicle with a lifter is thereby downsized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of the transport vehicle in a first example. 
         FIG. 2  is a schematic perspective view of the frame and the lifter mechanisms of the transport vehicle. 
         FIG. 3  is a schematic sectional view of the lifter mechanisms. 
         FIG. 4  is a schematic perspective view of the frame of the transport vehicle. 
         FIG. 5  is a schematic perspective view of the frame viewed from below. 
         FIG. 6  is a schematic plain view of a relationship between the frame and the electrical components. 
         FIG. 7  is a schematic perspective view of the lower frame attached to the vehicle body frame, viewed from below. 
         FIG. 8  is a schematic perspective view of the lower frame detached from the vehicle body frame, viewed from below. 
     
    
    
     REFERENCE SIGNS LIST 
     
         
           1 : transport vehicle 
           3   a : vehicle body frame 
           3   b : vehicle body frame 
           4 : upper portion frame 
           5   a : driving wheel 
           5   b : driving wheel 
           6 : side frame 
           7   a : auxiliary wheel 
           7   b : auxiliary wheel 
           7   c : auxiliary wheel 
           7   d : auxiliary wheel 
           8   a : travelling motor 
           8   b : travelling motor 
           9   a : lifter mechanism 
           9   b : lifter mechanism 
           9   c : lifter mechanism 
           9   d : lifter mechanism 
           11 : connection frame 
           13 : lower frame 
           17 : electrical component 
           21   a : elevating motor 
           21   b : elevating motor 
           22   a : distribution mechanism 
           22   b : distribution mechanism 
           23 : elevating transmission shaft 
           23   a : flat plate portion 
           24   a : driving shaft 
           24   b : driving shaft 
           24   c : driving shaft 
           24   d : driving shaft 
           25 : bearing 
           26 : housing 
           27 : main body 
           28 : rack 
           29 : first reinforcement portion 
           30 : pinion 
           31   a : second reinforcement portion 
           31   b : second reinforcement portion 
           33   a : third reinforcement portion 
           33   b : third reinforcement portion 
           41 : turning table 
       
    
     DETAILED DESCRIPTION 
     1. First Example 
     (1) Basic Configuration 
     Referring to  FIGS. 1 through 3 , a basic configuration of a transport vehicle  1  will be explained.  FIG. 1  is a schematic perspective view of the transport vehicle in the first example.  FIG. 2  is a schematic perspective view of the frame and the lifter mechanisms of the transport vehicle.  FIG. 3  is a schematic sectional view of the lifter mechanisms. 
     The transport vehicle  1  is a device for transporting an article. The transport vehicle  1  can transport the article to a transfer location and elevate it. In addition, the transport vehicle  1  can turn the article around a vertical axis. The transport vehicle  1  includes a pair of right and left vehicle body frames  3   a ,  3 , driving wheels  5   a ,  5   b , auxiliary wheels  7   a ,  7   b ,  7   c ,  7   d , and lifter mechanisms  9   a ,  9   b ,  9   c ,  9   d.    
     The right and left vehicle body frames  3   a ,  3   b  extend forward and backward in a first direction (front and back direction), and are located apart from each other in a second direction perpendicular to the front and back direction. The vehicle body frames  3   a ,  3   b  are composed of thin and flat members. 
     The driving wheels  5   a ,  5   b  are respectively disposed at middle portions in the first direction of the vehicle body frames  3   a ,  3   b . Accordingly, the total number of the driving wheels is two. A direction to which the driving wheels  5   a ,  5   b  face is a travelling direction in the first direction. The transport vehicle  1  includes travelling motors  8   a ,  8   b . The travelling motors  8   a ,  8   b  are direct drive type respectively installed in the driving wheels  5   a ,  5   b . The travelling motor  8   a  is hidden and is not shown in the figures. 
     The auxiliary wheels  7   a ,  7   b ,  7   c ,  7   d  are disposed at lower portions of end portions in the first direction of the vehicle body frames  3   a ,  3   b . Specifically, the auxiliary wheel  7   a  is disposed at a front end portion of the vehicle body frame  3   a , the auxiliary wheel  7   b  is disposed at a back end portion of the vehicle body frame  3   a , the auxiliary wheel  7   c  is disposed at a front end portion of the vehicle body frame  3   b , and the auxiliary wheel  7   d  is disposed at a back end portion of the vehicle body frame  3   b . The auxiliary wheel is a caster wheel, for example, and it can be turned around a vertical axis. 
     In this example, the auxiliary wheels  7   a  through  7   d  bear most of loads of the article and the transport vehicle  1  so that the load supported by one of the driving wheels  5   a ,  5   b  is about a fraction of load of one of auxiliary wheels  7   a  through  7   d  bear. The driving wheels  5   a ,  5   b  are urged below by springs (not shown), respectively. 
     The lifter mechanisms  9   a  through  9   d  are mechanisms that elevate the article. Specifically, the lifter mechanisms  9   a  through  9   d  are disposed at upper portions of end portions in the first direction of vehicle body frames  3   a ,  3   b . More specifically, the lifter mechanism  9   a  is disposed at a front end portion of the vehicle body frame  3   a , the lifter mechanism  9   b  is disposed at a back end portion of the vehicle body frame  3   a , the lifter mechanism  9   c  is provided at a front end portion of the vehicle body frame  3   b , and the lifter mechanism  9   d  is provided at a back end portion of the vehicle body frame  3   b.    
     According to this example, each of the auxiliary wheels is located deviated outward in the first direction of each of the corresponding lifter mechanisms. Since the auxiliary wheel is located outside of the lifter mechanism, it is preferable because the support by the auxiliary wheel becomes stable. 
     The location of the auxiliary wheel may correspond to the location of the lifter mechanism in planar view, and may be deviated inward in the first direction. The auxiliary wheel may be deviated from the lifter mechanism in the second direction (and not in the first direction), and may be deviated from the lifter mechanism in both the first direction and the second direction. The advantage of deviating the auxiliary wheel from the lifter mechanism in planar view is to ensure a space in which the elevating transmission shaft of the lifter mechanism can move in the vertical direction. 
     As described above, the locations on which lifter mechanisms  9   a  through  9   d  are provided are the vehicle body frames  3   a ,  3   b , which support the driving wheels  5   a ,  5   b  and the auxiliary wheels  7   a  through  7   d . Accordingly, it is possible to integrate the lifter mechanisms  9   a  through  9   d  with the vehicle body frames  3   a ,  3   b  so that the transport vehicle  1  can be downsized and lightened. 
     According to the transport vehicle  1 , in addition, since the lifter mechanisms  9   a  through  9   d  and the auxiliary wheels  7   a  through  7   d  are provided at the end portions in the first direction of the vehicle body frames  3   a ,  3   b , the lifter mechanisms  9   a  through  9   d  are located in the vicinity of the auxiliary wheels  7   a  through  7   d . Accordingly, a heavy load is unlikely to be applied to portions other than the end portions of the vehicle body frames  3   a ,  3   b  so that the transport vehicle  1  can be downsized and lightened. 
     The transport vehicle  1  further includes a connection frame  11 . The connection frame  11  is a thin and flat member, and connects upper portions of the pair of right and left vehicle body frames  3   a ,  3   b  with each other. Specifically, the connection frame  11  has a thin and flat portion  11   a  extending in the second direction and is continuous with upper faces of the pair of right and left vehicle body frames  3   a ,  3   b , as shown in  FIGS. 4 and 5 . 
     The connection frame  11  includes, other than the thin and flat portion  11   a , other members that reinforce the pair of right and left vehicle body frames  3   a ,  3   b . For example, the connection frame  11  further includes a pair of ribs  11   b . The pair of ribs  11   b  is a thin and flat member fixed to lower portion at both ends in the first direction of the thin and flat portion  11   a , and extends in the second direction. Both ends in the second direction of the pair of ribs  11   b  are fixed to the side faces of the upper portion of a first reinforcement portions  29  (later described). In addition, the connection frame  11  includes a reinforcement member  11   c . The reinforcement member  11   c  is located at the lower portions of both ends in the second direction of the thin and flat portion  11   a  such that the reinforcement member  11   c  is located between the pair of ribs  11   b . The reinforcement member  11   c  are fixed to the thin and flat portion  11   a  and the pair of ribs  11   b , and are further fixed to the first reinforcement portion  29 . 
     Accordingly an H-shaped upper portion frame  4  is constituted of the pair of right and left vehicle body frames  3   a ,  3   b  and the connection frame  11 . 
     According to the above-described structure, the upper portion frame  4 , which is constituted of the pair of the vehicle body frames  3   a ,  3   b  and the connection frame  11 , defines openings facing upwardly. As a result, it is easy to adjust or replace electrical components  17  (later described). In contrast, if a frame of the lifter mechanism is provided on the frame of the vehicle as before, the frame of the lifter mechanism hinders the access to the components installed inside. 
     According to the above-described structure, the connected portions by the connection frame  11  are the middle portions in the first direction of the pair of right and left vehicle body frames  3   a ,  3   b . Accordingly, in the transport vehicle  1 , which has a frame with a simple structure, enough strength is obtained. Especially when the transport vehicle  1  travels along a rough surface of the floor so that a large force is partially applied thereto, the stress is distributed because the pair of right and left vehicle body frames  3   a ,  3   b  are connected only at the middle portions in the first direction thereof so that the whole body is likely to bend. 
     In addition, since the lifter mechanisms  9   a  through  9   d  are provided at four corners of the transport vehicle  1  in planar view (corners of the H-shaped upper portion frame  4 ), a large space is defined between the pair of right and left vehicle body frames  3   a ,  3   b . Accordingly, it is easy to locate the electrical components  17  (later described). 
     The transport vehicle  1  includes elevating motors  21   a ,  21   b  as devices to drive a part or the whole of the lifter mechanisms. The elevating motors  21   a ,  21   b  are provided on the connection frame  11 . 
     The transport vehicle  1  includes distribution mechanisms  22   a ,  22   b  that respectively distribute power of the elevating motors  21   a ,  21   b  into two directions. 
     The transport vehicle  1  includes driving shafts  24   a ,  24   b  that extend from the distribution mechanism  22   a  respectively to the lifter mechanisms  9   a ,  9   b . The driving shafts  24   a ,  24   b  are rotatably supported respectively by bearings  32   a ,  32   b  provided on an upper face of the vehicle body frame  3   a.    
     The transport vehicle  1  includes driving shafts  24   c ,  24   d  that extend from the distribution mechanism  22   b  respectively to the lifter mechanisms  9   c ,  9   d . The driving shafts  24   c ,  24   d  are rotatably supported respectively by bearings  32   c ,  32   d  provided on an upper face of the vehicle body frame  3   b.    
     As a sample of the lifter mechanisms, a structure of the lifter mechanism  9   a  will be explained. As shown in  FIG. 3 , the lifter mechanism  9   a  includes an elevating transmission shaft  23 . The elevating transmission shaft  23  is an elevating member, and extends long in the vertical direction. The elevating transmission shaft  23  includes a flat plate portion  23   a  on an upper portion thereof. The elevating transmission shaft  23  is supported by a bearing  25  supported by a housing  26  of the lifter mechanism  9   a  such that the elevating transmission shaft  23  can move vertically but cannot rotate. 
     The elevating transmission shaft  23  includes a rack  28  extending in the vertical direction on a side face thereof. The driving shaft  24   a  includes a pinion  30  engaged with the rack  28 . Accordingly, rotation of the elevating motor  21   a  elevates the elevating transmission shaft  23 . 
     According to the transport vehicle  1 , since the elevating motors  21   a ,  21   b  are supported by the upper portion frame  4  too, it is possible to further downsize the transport vehicle  1 . 
     The transport vehicle  1  includes a lower frame  13 . The lower frame  13  is disposed between the pair of right and left vehicle body frames  3   a ,  3   b , and removably fixed to lower portions of the pair of right and left vehicle body frames  3   a ,  3   b . Specifically, the lower frame  13  is “a flat and rectangular, thin plate member,” and is fixed to inner portions in the second direction of the vehicle body frames  3   a ,  3   b  by screws (not shown). According to the transport vehicle  1 , as described above, since the vehicle body frames  3   a ,  3   b  and the lower frame  13  constitute a dividing structure, it is easy to access the electrical components  17  (later described). 
     The transport vehicle  1  includes electrical components  17 . The electrical components  17  are located on an upper face of the lower frame  13 , but the positions of the electrical components  17  are different from that of the connection frame  11  in planar view. The electrical components  17  include batteries and motor drivers, for example. 
     The transport vehicle  1  includes a turning table  41 . The turning table  41  is a device that rotates an article (not shown) around the vertical axis. The turning table  41  is provided on the upper sides of the lifter mechanisms  9   a  through  9   d.    
     (2) Detailed Explanation of the Frames 
     Referring to  FIGS. 4 and 5 , a structure of the vehicle body frames will be explained in detail.  FIG. 4  is a schematic perspective view of the frames of the transport vehicle.  FIG. 5  is a schematic perspective view of the frames viewed from below. 
     Each of the vehicle body frames  3   a ,  3   b  includes a main body  27  having a horizontal surface and extending in the front and back direction, and a first reinforcement portion  29  extending below from the main body  27 . 
     According to the transport vehicle  1 , since each of the vehicle body frames  3   a ,  3   b  includes the first reinforcement portion  29 , the strength is improved while keeping the light weighting. 
     More specifically, the first reinforcement portion  29  is a thin and flat member functioning as a rib, and extends below from almost the whole of the inner edge in the second direction of the main body  27 . The lower frame  13  is fixed to a lower edge of the first reinforcement portion  29 . 
     More specifically, each of the vehicle body frames  3   a ,  3   b  has second reinforcement portions  31   a ,  31   b . The second reinforcement portions  31   a ,  31   b  are thin and flat members functioning as ribs, and are provided below the vehicle body frames  3   a ,  3   b  at positions close to and inward in the first direction from portions on which the lifter mechanisms  9   a  through  9   d  are provided. The second reinforcement portions  31   a ,  31   b  extend below from the main body  27 , and extend from the first reinforcement portion  29  to the opposite edge in the second direction. 
     More specifically, each of the vehicle body frames  3   a ,  3   b  includes third reinforcement portion  33   a ,  33   b . The third reinforcement portions  33   a ,  33   b  are thin and flat members functioning as ribs, and are located below the vehicle body frames  3   a ,  3   b  at positions close to and outward in the second direction from portions on which the lifter mechanisms  9   a  through  9   d  are provided. The second reinforcement portions  31   a ,  31   b  extend below from the main body  27 , and extend outward in the first direction from the outer edge in the second direction of the second reinforcement portions  31   a ,  31   b.    
     As described above, the first reinforcement portion  29 , the second reinforcement portion  31   a , and the third reinforcement portion  33   a  are located to encompass a portion on which the lifter mechanisms  9   a  through  9   d  are provided. Accordingly, the rigidity of the vehicle body frames  3   a ,  3   b  around the lifter mechanisms  9   a  through  9   d  is higher. 
     (3) Layout of the Electrical Components 
     Referring to  FIGS. 6 through 8 , a layout of the electrical components  17  will be explained.  FIG. 6  is a schematic plain view of a relationship between the frame and the electrical components.  FIG. 7  is a schematic perspective view of the lower frame attached to the vehicle body frame, viewed from below.  FIG. 8  is a schematic perspective view of the lower frame detached from the vehicle body frame, viewed from below. 
     As shown in  FIG. 6 , the electrical components  17  are located at positions different from that of the connection frame  11  in planar view. Accordingly, as shown in  FIG. 7 , it is possible to position the electrical components  17  at the same level with the main body  27  of the vehicle body frames  3   a ,  3   b  and the connection frame  11  (both are overlapped viewed from the side), thereby making the transport vehicle  1  compact in the height direction. 
     Next, an operation of detaching the lower frame  13  from the pair of right and left vehicle body frames  3   a ,  3   b  will be explained. When the vehicle body frames  3   a ,  3   b  are lifted, as shown in  FIG. 8 , the lower frame  13  leaves below as an integral member itself from the pair of right and left vehicle body frames  3   a ,  3   b . As described above, since the vehicle body frames  3   a ,  3   b  and the lower frame  13  constitute the dividing structure, the lower frame  13  and the electrical components  17  can be detached below from the vehicle body frames  3   a ,  3   b  with one action. In other words, the maintainability is improved. When the assembly work is performed, a process for the vehicle body frames  3   a ,  3   b  and a process for the lower frame  13  can be performed in parallel, thereby shortening the manufacturing time. Furthermore, the lower frame  13  and the electrical components  17  can be detached as an integral member, it is easy to process wirings. 
     2. Features of the Example 
     The above-described example can be explained as below. 
     The transport vehicle  1  (one example of the transport vehicle) includes a pair of right and left vehicle body frames  3   a ,  3   b  (one example of the vehicle body frames), driving wheels  5   a  through  5   b  (one example of the driving wheels), auxiliary wheels  7   a  through  7   d  (one example of the auxiliary wheels), lifter mechanisms  9   a  through  9   d  (one example of the lifter mechanisms). 
     The pair of right and left vehicle body frames  3   a ,  3   b  extend forward and backward in the first direction (one example of the front and back direction). 
     The driving wheels  5   a ,  5   b  are disposed in middle portions in the first direction of the vehicle body frames  3   a ,  3   b.    
     The auxiliary wheels  7   a  through  7   d  are disposed at lower portions of end portions in the first direction of the vehicle body frames  3   a ,  3   b.    
     The lifter mechanisms  9   a  through  9   d  are disposed at upper portions of end portions in the first direction of the vehicle body frames  3   a ,  3   b.    
     According to the transport vehicle  1 , positions on which the lifter mechanisms  9   a  through  9   d  are placed are the vehicle body frames  3   a ,  3   b , which support the driving wheels  5   a ,  5   b  and the auxiliary wheels  7   a  through  7   d . Accordingly, it is possible to integrate the lifter mechanism  9   a  with the vehicle body frames  3   a ,  3   b , thereby downsizing and lightening the transport vehicle  1 . 
     According to the transport vehicle  1 , since the lifter mechanisms  9   a  through  9   d  and the auxiliary wheels  7   a  through  7   d  are respectively provided at the end portions in the first direction of the vehicle body frames  3   a ,  3   b , the lifter mechanisms  9   a  through  9   d  are provided in the vicinity of the auxiliary wheels  7   a  through  7   d , respectively. Accordingly, the heavy load is unlikely to be applied to a portion other than the end portions of the vehicle body frames  3   a ,  3   b , thereby downsizing and lightening the transport vehicle  1 . 
     3. Other Examples 
     One example was explained above, but this disclosure is not limited to that example, and various modifications are possible within a scope that does not depart from the spirit of the disclosure. In particular, the examples and modified examples disclosed herein can be arbitrarily combined as needed. 
     (1) Modifications of the Frames 
     Although the pair of right and left frames and the connection frame are integral with welding, for example, in the first example, they may be independent members fixed to each other as long as they are connected firmly to each other. 
     Although the connection frame connects the middle portions of the pair of right and left vehicle body frames to each other in the first example, the position of the connection frame is not limited as long as the upper face of the vehicle body frame has an opening. In other words, the pair of right and left vehicle body frames may be connected to each other through the connection frame, between the front ends in the first direction thereof, between the back ends in the first direction thereof, or between both thereof. 
     Although the whole of the lower frame leaves below from the vehicle body frame in the first example, the lower frame may be divided in the first direction so that the lower frame can be removed from the vehicle body frames by taking out forward and backward. In this example, the work is easy because it is not necessary to lift the transport vehicle main body. The lower frame may be a thick plate member, not a thin plate. 
     (2) Modifications of the Elevating Motors 
     Although each of the elevating motor is provided for the two lifter mechanisms in the first example, each of the elevating motors may be provided for one lifter mechanism. Although a plurality of elevating motors are provided in the first example, one elevating motor may drive all of the lifters. 
     (3) Modifications of the Lifter Mechanisms 
     Although the lifter mechanism utilizes the rack and pinion in the first example, other structures may be used as long as it is able to elevate an article. In other words, the lifter may utilize a ball screw, a cylinder, or other elevating mechanisms. Although the elevating motors are provided on the connect frame in the first example, the elevating motors may be provided on the vehicle body frame. 
     (4) Modifications of the Auxiliary Wheels 
     Although the number of the auxiliary wheels is four in the first example, a pair of auxiliary wheels may be located at the front position and the back position.