Abstract:
The safety of a load carrying device has been enhanced by providing interactive mechanisms to ascertain the operations in predetermined manner. The enhanced safety mechanisms interactively force the operator to ascertain safety while an object such as a battery is loaded onto or unloaded from a predetermined structure such an industrial vehicle. The carrying device is engaged with the industrial vehicle during the loading or unloading task. In addition, the object is locked during the transportation. These safety features are mechanically ascertained.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention generally relates to a safety enhanced load carrier device and more particular relates to some enhanced safety features of the battery carrier device for transporting batteries to and from a vehicle including an industrial vehicle, an electric vehicle and a hybrid automobile.  
         [0002]     In the prior art technologies of small load carriers, safety features have been of some concern. In one approach in assuring safety during the transport, a load such as a battery is secured to a carrying device as disclosed in Japanese Patent Publication Hei 6-329240. For example, referring to  FIG. 1 , a carrier  1  is a hand-push device that includes a set of eight surface rollers  3  for facilitating the movement of a load in and out of the load carrying surface  4 . After the load such as a battery is rolled onto the load carrying surface  4 , a handle  8   a  is rotated in a clockwise direction to place a load block plate  6  above the load carrying surface  4 . The load block plate  6  prevents the forward movement of the load beyond the load block plate  6  while the user pushes the carrier  1  on four casters  2  by a handle  19  to a destination.  
         [0003]     In further details,  FIGS. 2A, 2B  and  2 C illustrate the safety mechanism that is linked to a ground stopper of the carrier  1 .  FIG. 2A  shows a relevant portion of one safety feature mechanism of the above prior art hand carrying device  1  of  FIG. 1 . The load block plate  6  extends above the surface rollers  3 , and the load block plate  6  is mechanically connected to the handle  8   a  at the other end of the carrier  1 .  
         [0004]     As shown in  FIG. 2B , when the handle  8   a  is rotated in the counter clockwise direction as shown in an arrow to place the load block plate  6  below the surface rollers  3  to remove the restricted movement of the load, the handle  8   a  cannot be turned all the way since a handle extended portion  17  hits a top portion  10   c  of a carrier stopper or stabilizer  10 . In order to place the load block plate  6  below the surface rollers  3 , the carrier  1  has to be initially secured or parked by the stopper  10 .  
         [0005]     As shown in  FIG. 2C , when the stopper  10  is placed in the park position, the stopper  10  is moved downwardly so that a bottom portion  10   a  makes a contact with the ground. Consequently, the top portion  10  is also downwardly moved by the same distance. This downward movement of the top portion  10   c  now allows the handle extended portion  17  to further rotate in the counter clock direction as shown by an arrow. When the handle  8   a  is rotated all the way to the left after the stopper  10  is grounded, the load block plate  6  is placed below the surface rollers  3  and the load is allowed to move forward beyond the load block plate  6 . As discussed above, the load is secured by the load block plate  6  during its transport, and the load block plate  6  is removed from its effective position only when the carrier is grounded. Unfortunately, the stopper  10  is freely activated or deactivated regardless of the relative location of the carrier  1  with respect to a predetermined desired destination or structure.  
         [0006]     In another approach in assuring safety during the transport, a load such as a battery is secured to a carrying device as disclosed in Japanese Patent Publication 2003-212125. For example, referring to  FIG. 3 , a carrier  20  is a hand-push device that includes a load carrying unit  22  with a set of casters  22   a  and a load transporting unit  24  with a set of casters  24   a . After the load such as a battery is placed on the load carrying unit  22 , the load carrying unit  22  itself is placed on the loading surface of the load transporting unit  24 . A pin  95  secures the load carrying unit  22  onto the load transporting unit  24  as the pin  95  is inserted into a position as indicated by the solid lines. As the operator pushes the carrier  20  by the handle  44  towards a desired destination such as a vehicle M, hooks  63  engages with the corresponding receiving structure in the vehicle M and completes the engagement as shown by the dotted line. The hooks  63  are mechanically linked to a hook control lever  80 , which moves between a predetermined hook engagement position  80 B and the hook releasing position  80 A.  
         [0007]     In further details of the second prior art approach,  FIG. 4  illustrates the safety mechanism that is associated with the control of the engagement hooks  63  of the carrier  20 . A pin  95  secures the load carrying unit  22  onto the load transporting unit  24  during the transportation. Upon reaching the desired destination, the operator removes the pin  95  that has been held in a hole  46 A and a semicircular hole  60 A and places it in a second hole  92 , which is located directly behind the hook control lever  80 . As the pin  95  is moved from the first hole  46 A to the second hole  92  by the operator, the load carrying unit  22  is still secured to the load transporting unit  24  by a temporary locking mechanism  99  and  28 . To release the load carrying unit  22  from the load transporting unit  24 , the temporary lock  99  must be manually released by the operator.  
         [0008]     During the movement of the load carrying unit  22  onto the vehicle M, if the pin  95  has been correctly inserted in the hole  92 , the engagement of the hooks  63  is secured by the pin  95  since the pin  95  blocks the backward movement of the hook control lever  80  to the hook releasing position  80 A of  FIG. 3 . However, as described above, the engagement hooks  63  are kept secured to the vehicle M by the manually inserted pin  95  in the hole  92  which is an independent act from the act of removing the pin  95  from the hole  60 A. In other words, one act does not guarantee to achieve the other act. Consequently, there is a margin of error in the safety mechanism for securing the hook engagement during the load delivery. Obviously, the margin of error depends upon the human operation to complete the above two independent acts. Furthermore, the operator also must manually releases the load carrying unit  22  from the load transporting unit  24  by the temporary lock  99  to further complicate the operation.  
         [0009]     As considered above in the two prior art approaches, the safety mechanism for the load carrying device remains to be desired. In general, the operator must perform independent acts, and these acts typically include securing the carrying device at a predetermined structure, unlocking the load, delivering the load to the desired structure or retrieving the load from the destination, locking the load and finally freeing the carrying device from the predetermined structure. Although these independent acts are important to maintain safety during the load transporting process, the operator often ignore or forget to perform each of these safety procedures. To realize effective safety features, the carrying device should be designed to eliminate the independent acts so that the operator is forced to follow predetermined safety procedures.  
       SUMMARY OF THE INVENTION  
       [0010]     In order to solve the above and other problems, according to a first aspect of the current invention, a safety device for carrying a load, including a load holding unit for holding a load, an engagement control located on the load holding unit for engaging the load holding unit with a predetermined structure in an engaged state and for disengaging the load holding unit from the predetermined structure in a disengaged state, and a load control located on the load holding unit for preventing the load from moving on the load holding unit in a load lock state, the load control freeing the load on the load holding unit in a load unlock state, the engagement control in the engaged state allowing the load control to transition into the load unlock state from the load lock state, the engagement control in the disengaged state prohibiting the load control from transitioning into the load unlock state from the load lock state.  
         [0011]     According to the second aspect of the current invention, a safety device for carrying a load, including a load holding unit for holding a load, an engagement control located on the load holding unit for engaging the load holding unit with a predetermined structure in an engaged state and for disengaging the load holding unit from the predetermined structure in a disengaged state, and a load control located on the load holding unit for preventing the load from moving on the load holding unit in a load lock state, the load control freeing the load on the load holding unit in a load unlock state, the load control in the load lock state allowing the engagement control to transition into the disengaged state from the engaged state, the load control in the load unlock state prohibiting the engagement control from transitioning into the disengaged state from the engaged state.  
         [0012]     According to the third aspect of the current invention, a method of operating a safety device for carrying a load, including the steps of a) engaging a load carrying unit with a predetermined structure so that a engagement control to be in an engaged state, b) placing a load control in a load unlock state while the engagement control is in the engaged state, c) performing a predetermined task with respect to the load, d) preventing the engagement control from transitioning to the disengaged state from the engaged state during the steps b) and c), e) placing the load control in a load lock state upon completing the step c) while the engagement control is still in the engaged state, and  0  disengaging the load carrying unit from the predetermined structure so that the engagement control is in a disengaged state only after the step e).  
         [0013]     According to the fourth aspect of the current invention, a method of operating a safety device for carrying a load to a predetermined structure, including the steps of a) engaging a load carrying unit with the predetermined structure so that a engagement control to be in an engaged state, b) placing a load control in a load unlock state while the engagement control is in the engaged state, c) performing a predetermined task with respect to the load, d) placing the load control in a load lock state upon completing the step c) while the engagement control is still in the engaged state, e) disengaging the load carrying unit from the predetermined structure so that the engagement control is in a disengaged state only after the step d), f) transporting the load carrying unit to a predetermined destination from the predetermined structure while the load control in the load lock sate, and g) preventing the load control from transitioning to the load unlock state from the load lock state after the step e) and during the step f).  
         [0014]     According to the fifth aspect of the current invention, a safety load carrying device for carrying a load to be used with an existing load transferring device, including: a retrofitting load carrying unit for holding the load and having a retrofitting portion for retrofitting the existing load transferring device; an engagement control unit located on the retrofitting load carrying unit for engaging the retrofitting load carrying unit with the predetermined structure in an engaged state and for disengaging the retrofitting load carrying unit from the predetermined structure in a disengaged state; and a load control located on the retrofitting load carrying unit for locking the load on the retrofitting load carrying unit in a load lock state, the load control unlocking the load on the retrofitting load carrying unit in a load unlock state, the engagement control in the engaged state allowing the load control to transition into the load unlock state from the load lock state, the engagement control in the disengaged state prohibiting the load control from transitioning into the load unlock state from the load lock state.  
         [0015]     According to the sixth aspect of the current invention, a safety load carrying device for carrying a load to be used with an existing load transferring device, including: a retrofitting load carrying unit for holding the load and having a retrofitting portion for retrofitting the existing load transferring device; an engagement control unit located on the retrofitting load carrying unit for engaging the retrofitting load carrying unit with the predetermined structure in an engaged state and for disengaging the retrofitting load carrying unit from the predetermined structure in a disengaged state; and a load control located on the retrofitting load carrying unit for locking the load on the retrofitting load carrying unit in a load lock state, the load control unlocking the load on the retrofitting load carrying unit in a load unlock state, the load control in the load lock state allowing the engagement control to transition into the disengaged state from the engaged state, the load control in the load unlock state prohibiting the engagement control from transitioning into the disengaged state from the engaged state.  
         [0016]     These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a prior art hand-push carrier device that includes a set of eight surface rollers for facilitating the movement of a load in and out of the load carrying surface.  
         [0018]      FIGS. 2A, 2B  and  2 C illustrate the safety mechanism of the prior art device of  FIG. 1  that is linked to a ground stopper of the carrier.  
         [0019]      FIG. 3  is a prior art hand-push carrier device that includes a load carrying unit with a set of casters and a load transporting unit with a set of casters.  
         [0020]     FIGS.  4  illustrates the safety mechanism of the prior art device of  FIG. 3  that is associated the control of the engagement hooks of the carrier.  
         [0021]      FIG. 5  is a prospective view illustrating a first preferred embodiment of the safety enhanced load carrying device according to the current invention.  
         [0022]      FIG. 6  is a side view illustrating the relative heights between the load transporting unit and the load carrying unit in one preferred embodiment according to the current invention.  
         [0023]      FIG. 7  is a prospective view illustrating one preferred embodiment of the load transporting unit and the load carrying unit that are joined together according to the current invention.  
         [0024]      FIG. 8  is a cross sectional view illustrating an engagement securing mechanism for safely maintaining the relative location of the load transporting unit and the load carrying unit in one preferred embodiment according to the current invention.  
         [0025]      FIGS. 9A and 9B  are perspective views illustrating the detailed mechanism for securing the load transporting unit and the load carrying unit of the first preferred embodiment according to the current invention.  
         [0026]      FIG. 10  is a prospective view illustrating one exemplary application of the first preferred embodiment according to the current invention.  
         [0027]      FIG. 11  is a prospective view isolating some mechanical components of the hook engagement system in the first preferred embodiment according to the current invention.  
         [0028]      FIG. 12  is a partial cross sectional view isolating other mechanical components of the hook engagement system in the first preferred embodiment according to the current invention.  
         [0029]      FIG. 13  is a prospective view isolating other mechanical components of the hook engagement system in the first preferred embodiment according to the current invention.  
         [0030]      FIG. 14  is a side view illustrating the positional relationship among the certain isolated components of the safety mechanisms in the first preferred embodiment according to the current invention.  
         [0031]      FIG. 15  is a prospective view isolating the components of the previously described safety mechanisms for the load lock control and the hook engagement control in the first preferred embodiment according to the current invention.  
         [0032]      FIG. 16  is a side view illustrating the interactive safety features between the load control and the engagement control in the first preferred embodiment according to the current invention.  
         [0033]      FIG. 17  is a side view illustrating other interactive safety features between the load control and the engagement control in the first preferred embodiment according to the current invention.  
         [0034]      FIG. 18  is a side view illustrating yet another interactive safety features between the load control and the engagement control in the first preferred embodiment according to the current invention.  
         [0035]      FIGS. 19A and 19B  are flow charts illustrating steps involved in a preferred process of operating the safety enhanced load carrying device according to the current invention.  
         [0036]      FIG. 20  is a prospective view illustrating a second preferred embodiment of the safety enhanced load carrying device according to the current invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]     Based upon incorporation by external reference, the current application incorporates all disclosures in the corresponding foreign priority applications (Japanese Applications 2004-2766653, 2004-283775, 2004-283776 and 2004-283839) from which the current application claims priority.  
         [0038]     In the following detailed description of the preferred embodiments, the word, “automobile” or “vehicle” is interchangeably used to include various types including conventional, electric and hybrid powered transportation devices for both industrial and non-industrial uses.  
         [0039]     Referring now to the drawings, wherein like reference numerals designate corresponding structures throughout the views, and referring in particular to  FIG. 5 , a prospective view illustrates a first preferred embodiment of the safety enhanced load carrying device according to the current invention. The first preferred embodiment of the safe load carrying device includes a load carrying unit  200  that carries a load such as a battery for an automobile and a load transporting unit  100  that carries the load carrying unit  200 . These units  100  and  200  are detachably connected as will be later discussed in detail, but they are independent and separate units. For example, multiple types of the load carrying units  200  are implemented for various load specifications but may be transported by a single type of the load transporting unit  100  in certain applications. In this regard, it is also possible that a certain preferred embodiment of the load carrying unit  200  is retrofitted on an existing one of the load transporting units  100 .  
         [0040]     Still referring to  FIG. 5 , the load carrying unit  200  further includes the following major components to safely transport the load. In general, the load carrying unit  200  has a load carrying or holding surface  200 S, load supporting legs  240 , engagement control units  290 ,  270  and load control units  310 ,  320 ,  322 . The load is placed on the load holding surface  200 S that is partially defined by a set of four rollers  220  to facilitate the movement of the load in and out of the load carrying surface  200 S. The rollers  220  are supported by a pair of opposing side walls  210 . The load holding surface  200 S and the associated structures are supported by a set of four legs  240 , which extend under the load holding surface  200 S to provide a ground clearance space. The ground clearance space has a predetermined carrier width E and a predetermined carrier height C as each shown by a corresponding double-headed arrow. Lastly, the load carrying unit  200  further includes a guiding pin  330  that is located at a front end to guide a relative position of the load carrying unit  200  with respect to a predetermined structure at the destination.  
         [0041]      FIG. 5  additionally illustrate some components for the safety features. In general, the engagement control is in either an engaged state or a disengaged state. The engagement control includes a movable control lever  290  that is mechanically connected to a pair of hooks  270 . The movable control lever  290  controls the hooks  270  to be placed at a predetermined engaged position or a predetermined disengaged position. The hooks  270  are designed to engage with a predetermined structure at the predetermined engaged position while the engagement control is in the engaged state as will be later described. Similarly, in general, the load control is in either a load lock state or a load unlock state. The load control includes a load control rotatable handle  320  that is mechanically connected to a load block plate  310  via a link rod  322 . The rotatable handle  320  controls the load block plate  310  to be placed at a predetermined load lock position or a predetermined load unlock position. The load block plate  310  is designed to block the movement of the load on the load carrying surface  200 S at the predetermined load lock position while the load control is in the load lock state as will be later described.  
         [0042]     The other half of the first preferred embodiment is the load transporting unit  100  as illustrated in the left side of  FIG. 5 . In general, the load transporting unit  100  is a hand track or a hand pallet tack that is commercially available or custom-manufactured according to a predetermined engineering specification. Exemplary commercial units are MiniMover BT-HB Series models or Hand Pallet BT-HP23 both from Toyota L&amp;F, Japan. The load transporting unit  100  further includes a fork area or load carrying area  110  and a set of wheels  130  and  140 . The fork or load carrying area  110  includes a fork insertion part in this embodiment. A pair of wheels  140  is located at one end of the load transporting unit  100  to steer the directions by a pulling handle  150 . Another pair of the rollers  130  is located apart by a certain distance near the other end of the load transporting unit  100  to balance the load carrying unit  200 . As the handle  150  is pumped vertically, the fork areas  110  are lifted from the ground. The handle  150  is also equipped with a break  180  for parking the load transporting unit  100  and a lift shifter  170  for reducing the lifted height of the fork areas  110  towards a predetermined fork default height A.  
         [0043]     Still referring to  FIG. 5 , the load carrying unit  200  is designed to be placed on the load transporting unit  100 . The fork areas  110  are inserted into the ground clearance space of the load carrying unit  200  as indicated by an arrow. The ground clearance space is designed to accommodate the load transporting unit  100  so that the fork areas  110  are placed underneath the load carrying unit  200  before the fork areas  110  are lifted to support the load carrying unit  200 . In other words, a fork width D is narrower than the predetermined carrier width E of the load carrying unit  200 . In addition, at the insertion time, the fork areas  110  are placed at the fork predetermined default height A that is lower than the predetermined carrier height C. The above described structures substantially facilitate the operator to interchange the load carrying units  200  that are placed on the ground with a single set of the load transporting unit  100 .  
         [0044]     Now referring to  FIG. 6 , a side view illustrates the relative height of the load transporting unit  100  and the load carrying unit  200  in one preferred embodiment according to the current invention. The load carrying unit  200  has the load holding area  200 S that is substantially the same height as the top of the rollers  220 . The rollers  220  are supported by the side plates  210 . The safety features of the load carrying unit  200  further includes the engagement control with the hooks  270  and the movable control lever  290  as well as the load control with the rotatable handle  320 , the link rod  322  and the load block plate  310 . The load holding surface  200 S is elevated by the supporting legs  240  to have the ground clearance space, and a distance from the ground G to a top portion  240   a  is indicated by a height C. The ground clearance height C is fixed.  
         [0045]     On the other hand, the height of the fork areas  110  is adjustable in the load transporting unit  100 . The adjustable ranges from the lowest predetermined fork default height A as indicated by the solid lines to an elevated height B as indicated by the dotted lines. As already described with respect to  FIG. 5 , the height of the fork areas  110  from the ground G is adjusted by pumping the handle  150  in the vertical direction. It is designed that the highest elevated height B exceeds the ground clearance height C. In order to insert the fork areas  110  in the ground clearance space of the load carrying unit  200 , the height of the fork areas  110  is adjusted below the ground clearance height C. Then, after the insertion, the height of the fork areas  110  has to be adjusted above the ground clearance height C to lift the load carrying unit  200  off the ground G in order to transport the load carrying unit  200  to a desired destination.  
         [0046]     Now referring to  FIG. 7 , a prospective view illustrates one preferred embodiment of the load transporting unit  100  and the load carrying unit  200  that are joined together according to the current invention. Generally, the load carrying unit  200  is supported by the load transporting unit  100  by placing the load carrying unit  200  on top of the fork areas  110  of the load transporting unit  100 . The front side of the load carrying unit  200  having the hooks  270  and the guide pin  330  is placed on a far side of the fork areas  110  away from the handle  150  of the load transporting unit  100 . This is because the far side is placed closer to a predetermined structure so that the guide pin  330  will guide the load carrying unit  200  to a predetermined structure. For example, the guide pin  330  will guide to a desired position by being inserted into a complementary hole on the predetermined structure. As the load carrying unit  200  arrives at the predetermined structure, the hooks  270  engage with a certain portion of the predetermined structure.  
         [0047]     The other side of the load carrying unit  200  having the movable control lever  290  and the load control rotatable handle  320  is placed on a near side of the fork areas  110  of the load transporting unit  100 . This side is a control side which should be easily accessible to the operator, and the operator controls the moving direction of the load transporting unit  100  and the load carrying unit  200  by steering the handle  150  towards the desired structure. During the transport, the movement of a load is limited by the load block plate  310  that is placed at the front end of the load holding surface. Upon arriving at the desired structure, the operator controls the safety features such as the hook engagement by the movable control lever  290  and the load locking by the rotatable handle  320 . Then, the operator moves the load towards the predetermined structure for delivery or towards the load carrying unit  200  for retrieval. Since the operator is standing away from the moving load and has easy access to all of the controls, the safety is promoted.  
         [0048]     Still referring to  FIG. 7 , during the transport of the load carrying unit  200 , there are other safety features in one preferred embodiment of the load transporting unit  100  and the load carrying unit  200  that are joined together according to the current invention. For example, the load carrying unit  200  is restricted from its lateral movement by the supporting legs  240 , whose inner side surfaces contact the corresponding side walls of the fork areas  110 . In addition, the load transporting unit  100  and the load carrying unit  200  are further securely joined together by certain additional mechanisms that will be explained with respect to  FIG. 8 .  
         [0049]     Now referring to  FIG. 8 , a cross sectional view illustrates an engagement securing mechanism for safely maintaining the relative location of the load transporting unit  100  and the load carrying unit  200  in one preferred embodiment according to the current invention. One of the supporting legs  240  is located at the front end of the load carrying unit  200 . The supporting leg  240  has a top wall  240 A and a side wall  240 B. On an inner surface of the top wall  240 A, a top fitting area  290  protrudes towards the ground surface G. In addition, the top wall  240 A and the side wall  240 B share a front fitting area  280  on their inner surfaces. The fork area  110  of the load transporting unit  100  has an opening  110 A near the wheel  130 . The front of the wheel  130  is a fork front portion  110 B as shown in the right side of the wheel  130  in the drawing. The distance between the front end of the top fitting area  290  and the front fitting area  280  corresponds to the length of the fork front portion  110 B of the fork area  110 .  
         [0050]     Still referring to  FIG. 8 , the engagement is secured among the fork front portion  110 B, the top fitting area  290  and the front fitting area  280  in the first preferred embodiment according to the current invention. As the front fork portion  110 B is inserted into the supporting leg  240  as indicated by a horizontal arrow and is also lifted to a position  110 ′ as indicated by a vertical arrow, the fork front portion  110 B reaches an secured position  110 B′ as indicated by the dotted line. The wheel  130  remains on the ground G at the same height after the lift. At the elevated position, the top fitting area  290  is placed in the opening  110 A′ of the position  110 ′. In the above described joined position, the fork front portion  10 B′ is secured by the front fitting area  280  to prevent the forward movement of the fork area  110  and also by the top fitting area  290  to prevent the backward movement of the fork area  110 . The fork areas  110  are further lifted beyond the elevated position  110 ′ in the dotted lines so that the supporting leg  240  is off the ground G for transporting the load carrying unit  200 . As described above, the fork areas  110  of the load transporting unit  100  and the supporting leg  240  of the load carrying unit  200  are securely joined during the transportation of the load.  
         [0051]      FIGS. 9A and 9B  illustrate a perspective view of the detailed mechanism for securing the load transporting unit  100  and the load carrying unit  200  of the first preferred embodiment according to the current invention. In particular,  FIG. 9A  illustrates the relevant components that are viewed from the bottom of the load carrying unit  200  before the secure engagement between the load transporting unit  100  and the load carrying unit  200 . The top fitting area  290  is located near a proximal edge on the inner surface of the top wall  240 A of the supporting leg  240 , and the proximal edge is closer to the rear of the load carrying unit  200  where the handle  150  is located. Although the top fitting area  290  is a rectangle that has a predetermined thickness in the first preferred embodiment, the shape and the thickness are not limited as long as the top fitting area  290  is mutually fitting to secure the load transporting unit  100 . The front fitting area  280  is located near a distal edge on the inner surface of the top wall  240 A, and the distal edge is closer to the front of the load carrying unit  200  where the hooks  270  are located. Although the front fitting area  280  is a rectangle that is perpendicular to the top wall  240 A in the first preferred embodiment, the shape and the orientation are not limited as long as the front fitting area  280  secures the load transporting unit  100 .  
         [0052]      FIG. 9B  illustrates the above relevant components that are viewed from the bottom of the load transporting unit  100  and the load carrying unit  200  after the secure engagement is made between the load transporting unit  100  and the load carrying unit  200 . After the front fork portion  110 B is inserted into the supporting leg  240 , the load transporting unit  100  is advanced towards the front end of the load carrying unit  200  until the load transporting unit  100  no longer can move forward. That is, a front end  10  of the fork area  110  makes a contact with the front fitting area  280 . Then, the load transporting unit  100  is lifted so that the area  110  is vertically moved to a predetermined secured position as described with respect to  FIG. 8 . The top fitting area  290  is now placed in the opening  110 A of the fork area  110  and detachably secures the relative position between the load transporting unit  100  and the load carrying unit  200 . Similarly, the front end  110 C now butts against the front fitting area  280 . Thus, the top fitting area  290  and the front fitting area  280  secure the relative position of the load transporting unit  100  and the load carrying unit  200  in a detachable manner.  
         [0053]     Now referring to  FIG. 10 , a prospective view illustrates one exemplary application of the first preferred embodiment according to the current invention. As described above with respect to  FIGS. 5 through 10 , a predetermined load M such as a battery can be delivered to or retrieved from a desired destination such as a vehicle  410 . The vehicle  410  includes various types of vehicles as defined above. In a particular example as illustrated in  FIG. 10 , the battery pack M is currently situated inside a forklift  410  as indicated in the solid lines. The battery pack M is to be retrieved from the forklift  410  onto the load carrying unit  200  at a position M′ as indicated by the dotted. lines. It is needless to say that the delivering process is substantially reversed from retrieving the battery pack from the position M inside the vehicle  410  to at the position M′.  
         [0054]     Still referring to  FIG. 10 , to further illustrate the retrieval process, the load transporting unit  100  and the load carrying unit  200  are operated in the following manner. An empty one of the load carrying units  200  is securely jointed onto the load transporting unit  100  as described with respect to  FIGS. 8 and 9 . After securely joining the empty load carrying units  200  on the load transporting unit  100 , the operator moves a joined structure  300  towards the forklift  410 . As the joined structure approaches the forklift  410 , the guide pin  330  is aimed at the corresponding receiving structure  430  on the forklift  410 . During the aiming process, the operator positions the joined structure  300  by steering the wheel  140  and adjusts the height of the joined structure  300  by the handle  150 . As previously described, the height from the ground increases by vertically pumping the handle  150  while the height decrease by releasing its height sustaining mechanism via the lever  170 . The complementary engagement between the guide pin  330  and the receiving structure  430  automatically assures the joined structure  300  to be positioned at a predetermined battery exchange location of the forklift  410 . As the joined structure  300  approaches the predetermined battery exchange height and location according to the guide pin  330 , the hooks  270  of the load carrying units  200  also initiate and complete the engagement with a hook engagement unit  420  of the forklift  410 . The appropriate engagement between the hooks  270  and the hook engagement unit  420  is completed when the joined structure  300  arrives at the predetermined battery exchange height and location which is immediately adjacent to the side of the forklift  410  as illustrated in  FIG. 10 . At the predetermined battery exchange position, the operator applies the parking break via the break lever  180  in order to secure the safe battery exchange position.  
         [0055]     At the safe battery exchange position, the operator controls additional safety mechanisms of the first preferred embodiment in order to ascertain an accident-free battery retrieval operation according to the current invention. Initially, the load control rotatable handle  320  is rotated in the clockwise direction so that the load block plate  310  is placed out of the load holding surface  200 S, and then the battery pack M′ is retrieved from the forklift  410  onto the load holding surface  200 S at a retrieving position M′ as indicated by the dotted lines. Upon confirming the appropriate retrieving position M′, the operator secures the battery pack M′ on the load carrying units  200  by rotating the rotatable handle  320  in the counterclockwise direction so that the load block plate  310  is placed at the front end of the load holding surface  200 S for blocking the forward movement of the battery pack M′. After the operator confirms the secured battery pack M′, he or she now disengages the hooks  270  from the hook engagement unit  420  of the forklift  410  before moving the joined structure  300  to a desired destination. The hook disengagement is accomplished by pulling the movable lever towards the handle  150 . The above described safety feature mechanisms will be further illustrated in detail in the following description of the preferred embodiment.  
         [0056]     Now referring to  FIG. 11 , a prospective view isolates some mechanical components of the hook engagement system or the engagement control in the first preferred embodiment according to the current invention. As described above with respect to  FIG. 10 , the hooks  270  are positioned either at a predetermined engaged position or a predetermined disengaged position via the movable control lever  290 . The movable control lever  290  is at a control engaged position  292 A as illustrated by the solid lines when an engagement control  400  is in the engaged state. That is, when the movable control lever  290  of the engagement control  400  is in the engaged state, the hooks  270  are positioned at the predetermined engaged position as shown in the solid lines. In general, the hooks  270  are positioned in the engaged position by the urging caused by the spring  272 .  
         [0057]     Still referring to  FIG. 11 , on the other hand, when the operator pulls the movable control lever  290  as indicated by an arrow to a position  290 C, the movable control lever  290  is at a control disengaged position as illustrated by the dotted lines as the engagement control  400  transitions into the disengaged state. Due to the pulling action, the movable control lever  290  causes a first linkage rod  294  to rotate in the counterclockwise direction as indicated by an arrow. The rotation of the first linkage rod  294  pushes a first linkage arm  295  and a second linkage rod  296  to a forward direction as indicated by an arrow. Lastly, the forward movement of the second linkage rod  296  causes a second linkage arm  297  and a third linkage rod  298  to rotate in the counter clockwise direction as indicated by an arrow against the urging of the spring  272 . Consequently, when the movable control lever  290  of the engagement control  400  is in a disengaged state, the hooks  270  are positioned into the predetermined disengaged position  270 A as shown in the dotted lines and the corresponding arrows.  
         [0058]     Now referring to  FIG. 12 , a partial cross sectional view isolates other mechanical components of the hook engagement control system in the first preferred embodiment according to the current invention. As described above with respect to  FIG. 11 , the hooks  270  are positioned either at the engaged position as shown by solid lines or the disengaged position  270 A as shown in the dotted lines. In general, the hooks  270  are positioned in the engaged state by the urging caused by the spring  272  as described with respect to  FIG. 11 . The operator maneuvers the load carrying unit  200  towards the predetermined target position via the engagement of the guide pin  330  with the corresponding receiving structure as indicated by an arrow. At the same time, as the hooks  270  approach the predetermined structure  410 , the hooks  270  remain in the predetermined engaged position. Upon contacting the hook engagement unit  420 , the further forward movement of the load carrying unit  200  by the operator causes the hooks  270  to push upward by their sloped portion against the urging and the weight of the hooks  270  and rotate around the third linkage rod  298 . Subsequently, a vertical portion of the hooks  270  engages with the corresponding wall of hook engagement unit  420  to complete the correct positioning of the load carrying unit  200  in a secured manner.  
         [0059]     Now referring to  FIG. 13 , a prospective view isolates other mechanical components of the hook engagement system in the first preferred embodiment according to the current invention. In particular, the prospective view illustrates the components associated with the movable control lever  290  for locking the disengaged state of the engagement control. The movable control lever  290  and the first linkage rod  294  are fixedly connected by a linkage connecting plate or a rotation preventing plate  290 D. As described above with respect to  FIG. 11 , the movable control lever  290  is pulled forward or backward to cause the rotation of the first linkage rod  294  via the linkage connecting plate  290 D as indicated by a double-headed arrow. The rotation of the first linkage rod  294  ultimately places the hooks to be at a desired position. In dependent of the above described movement for positioning the hooks, the movable control lever  290  also provides additional safety features during the operation.  
         [0060]     Still referring to  FIG. 13 , the movable control lever  290  further includes additional components for controlling the movements of the movable control lever  290 . A receiving portion  293  receives a vertical portion  290 A in its inner space at a proximal end. A distal end  290 E of the vertical portion  290 A extends beyond a distal end of the receiving portion  293 . The vertical portion  290 A is movable inside the receiving portion  290 B of the movable control lever  290 . The vertical portion  290 A further includes a position pin  290 B that is fixed on the vertical portion  290 A and protrudes from the surface of the vertical portion  290 A. The receiving portion  293  also further includes a short groove  293 A and a long groove  293 B for accepting the position pin  290 B. Both the short groove  293 A and the long groove  293 B start on the edge of the proximal end of the receiving portion  293 , but the long groove  293 B further extends downwardly beyond the short groove  293 A. At a position  292 A as indicated by the solid lines, the rotatable knob  292  is positioned so that the position pin  290 B is accepted by the short groove  293 A. At a position  292 B as indicated by the dotted lines, the rotatable knob  292  is positioned so that the position pin  290 B is accepted by the long groove  293 B. The position pin  290 B is prevented from rotating further beyond a certain point by a pin blocking plate  293 C. Thus, a rotatable knob  292  of the movable control lever  290  is rotatable for approximately  90  degrees along the surface that is perpendicular to a vertical portion  290 A of the movable control lever  290  as indicated by a double-headed arrow.  
         [0061]     At the position pin  292 B, the position pin  290 B is accepted by the long groove  293 B, and the movable control lever  290  moves further downwardly by the following mechanism. Near the distal end  290 E, a stopper pin  293 H is located on the vertical portion  290 A. A spring  293 F and a pair of washers  293 E,  293 G are placed on the vertical portion  290 A between the stopper pin  293 H and the distal end of the receiving portion  293 . Since the spring  293 F urges the washers  293 E and  293 G apart respectively towards the distal end of the receiving portion  293  and the stopper pin  293 H, when the position pin  290 B is accepted by the long groove  293 B, the distal end  290 E is urged to move towards an extended position as indicated by the dotted lines. Consequently, the rotatable knob  292  of the movable lever  290  automatically moves downwardly from the position  292 B to the position  292 C as indicated by a downward arrow when the position pin  290 B is accepted by the long groove  293 B.  
         [0062]     On the other hand, when the rotatable knob  292  is moved from the position  292 C to  292 B by the operator against the urging caused by the spring  293 F as indicated by the upward arrow, the distal end  290 E of vertical portion  290 A is pulled back from the above described extended position by the following mechanism. As the vertical portion  290 A is pulled back, the stopper pin  293 H pushes the lower washer  293 G upwardly to compress the spring  293 F. Subsequently, after the rotatable knob  292  is rotated in the counter clockwise direction from the position  292 B to the position  292 A, the position pin  290 B is accepted by the short groove  293 BA. Consequently, the distal end  290 E is maintained at a retracted position as indicated by the solid lines and the spring  293 F remains in the compressed state.  
         [0063]     Now referring to  FIG. 14 , a side view illustrates the positional relationship among the certain isolated components of the safety mechanisms in the first preferred embodiment according to the current invention. The isolated side view is seen from the side of the load carrying unit  200  as indicated by an arrow in  FIG. 7 . As already described with respect to  FIG. 13 , the rotatable knob  292  rotates between the two positions  292 A and  292 C, and the rotatable knob  292  also changes its vertical position between the two positions  292 A and  292 C. At the position  292 C, the rotatable knob  292  is in the disengaged state for placing the hooks in the predetermined disengaged position. The rotatable knob  292  at the position  292 C is lowered by the urging from the spring  293 F as indicated by a downward arrow. The expanding spring  293 F forces the washers  293 E and  293 G apart to push the stopper pin  293 H on the vertical portion  290 A in the downward direction. As a result, the distal end  290 E of the vertical portion  290 A engages with a bore  153 A of a bottom plate  153 . Thus, when the movable control lever  290  is in the disengaged state, the above engagement mechanism locks the rotatable knob  292  in this position  292 C to maintain the hooks in the disengaged position. This locking mechanism provides a safety feature while the operator moves the load carrying unit  200  on the load transporting unit  100  away from the predetermined structure by maintaining the hooks  270  in the predetermined disengaged position.  
         [0064]     On the other hand, at the position  292 A, the rotatable knob  292  is in the engaged state as indicated by the dotted lines. As the rotatable knob  292  is rotated and pulled back towards the handle  150 , the movable control lever  290  causes the counter clockwise rotation of the first linkage rod  294  via the linkage connecting plate  290 D as indicated by an arrow. At the same time, at the position  292 A, the rotatable knob  292  is elevated by the operator against the spring  293 F. As a result, the distal end  290 E of the vertical portion  290 A disengages itself from the bore  153 A of the bottom plate  153 . Thus, when the movable control lever  290  is in the engaged state, the rotatable knob  292  in the position  292 A maintains the hooks in the predetermined engaged position.  
         [0065]     Still referring to  FIG. 14 , the side view also illustrates the positional relationship of other safety mechanisms in the first preferred embodiment according to the current invention. In general, the load control rotatable handle  320  controls the load locking mechanism or unit as described with respect to  FIGS. 5, 6 ,  7  and  10 . The rotatable handle assembly  320  of the load control is located adjacent to the movable control lever  290  of the hook engagement control and mechanically interacts with the load control. The rotatable handle assembly  320  further includes a load control knob  320 A that is attached to a spring  320 C and a safety pin  320 B. The rotatable handle assembly  320  is supported by a mounting bracket  320 D through a bore  320 E, and the mounting bracket  320 D is attached to a load control rotatable arm  320 G. The load control rotatable arm  320 G and the rotatable handle assembly  320  are designed to rotate around the link rod  322  to control the load lock.  
         [0066]      FIG. 14  also illustrates that an additional safety feature is provided for the load lock mechanism in the preferred embodiment according to the current invention. The safety pin  320 B extends through a bore  320 F of the load control rotatable arm  320 G and also beyond a proximal portion of the linkage connecting plate  290 D as indicated by the solid lines. In the attempt to rotate the load control rotatable arm  320 G and the rotatable handle assembly  320 , the operator must pull the safety knob  320 A away from the rotatable arm  320 G so that the safety pin  320 B clears the linkage connecting plate  290 D. The distance between the linkage connecting plate  290 D and the load control rotatable arm  320 G varies depending upon the position of the movable control lever  290 . The positional relation between the safety pin  320 B and the linkage connecting plate  290 D will be further described in detail with respect to  FIGS. 15, 16  and  18 .  
         [0067]     Now referring to  FIG. 15 , a prospective view isolates the components of the previously described safety mechanisms for the load lock control and the hook engagement control in the first preferred embodiment according to the current invention. The movable control lever  290  is located in front of the rotatable handle assembly  320 . As already described above with respect to  FIGS. 11, 12 ,  13  and  14 , the operator shifts the movable control lever  290  forward and backward in order to control the position of the hooks  270  via the linkages  294  through  298 . As also previously described, the rotatable handle assembly  320  of a load control  500  is located adjacent to the load control movable lever  290  of the hook engagement control  400  and mechanically interacts with the engagement control  400 . The rotatable load lock handle  320  of the load control  500  is at a predetermined lock position  320 A as illustrated by the solid lines when the load control  500  is in a predetermined load lock state. That is, when rotatable load lock handle  320  of the load control  500  is in the load lock state, the load block plate  310  is placed at the predetermined load lock position as shown in the solid lines to secure the load.  
         [0068]     Still referring to  FIG. 15 , on the other hand, when the operator rotates the rotatable load lock handle  320  as indicated by an arrow to a position  320 A′, the rotatable load lock handle  320  is at the predetermined load unlock position  320 A′ as illustrated by the dotted lines as the load control  500  transitions into a predetermined load unlock state. After the rotatable load lock handle  320  is rotated in the clockwise direction as indicated by an arrow to a rotated position  320 A′, the load block plate  310  is placed in the predetermined load unlock position  310 A as indicated by the dotted lines. As the rotatable knob  320 A reaches the rotated position  320 A′, a shift block plate or a disengagement block plate  340  as indicated by dotted lines is also placed at an upright position  340 A adjacent to the linkage connecting plate  290 D behind the movable control lever  290 . As a part of the additional safety features, the above described rotation of the rotatable load lock handle assembly  320  depends upon the position of the engagement control movable lever  290  as will be described with respect to  FIGS. 16,17  and  18 .  
         [0069]     Now referring to  FIG. 16 , a side view illustrates the interactive safety features between the load control and the engagement control in the first preferred embodiment according to the current invention. The isolated side view is seen from the side of the load carrying unit  200  as indicated by an arrow in  FIG. 7 . Certain components are not discussed here since the description has been already provided with respect to  FIG. 14 . As already described with respect to  FIG. 14 , the rotatable knob  292  at the position  292 A is in the engaged state, and the distal end  290 E of the vertical portion  290 A disengages itself from the bore  153 A of the bottom plate  153 . When the hook engagement control is in the engaged state, it is presumed that the load carrying unit  200  is securely engaged with a predetermined structure for delivering a load to the predetermined structure or retrieving a load from the predetermined structure. In other words, when the rotatable knob  292  of the engagement control is at the position  292 A, the rotatable handle assembly  320  of the load control can be rotated. Based upon the above presumption, the operator is allowed to unlock the block plate or stopper  310  on the load carrying unit  200  as discussed with respect to  FIG. 10 .  
         [0070]     Still referring to  FIG. 16 , safety features associated with the rotation of the rotatable load lock handle assembly  320  are further described for the first preferred embodiment according to the current invention. Despite the above presumption, when the operator actually attempts to rotate the rotatable load lock handle assembly  320 , the first preferred embodiment provides additional safety features by forcing the operator to pull the load control knob  320 A to a retracted position  320 A″ away from the linkage connecting plate  290 D as indicated by an arrow. As the load control knob  320 A is retracted to the retracted position  320 A″, the spring  320 C is compressed against the bracket  320 D, and the safety pin  320 B also moves through the bore  320 F in the same direction as indicated by an arrow. As a result of the above movement, a terminal end  320 B-T of the safety pin  320 B reaches its retracted position  320 B-T′ as indicated by the dotted line. At retracted position  320 B-T′, the safety pin  320 B clears the linkage connecting plate  290 D as the rotatable load lock handle assembly  320  is rotated around the linkage rod  322  as indicated by an arrow. Thus, despite the presumption on the hook engagement status, the additional feature forces the operator to ascertain safety by retracting the load control knob  320 A while rotating the rotatable load lock handle assembly  320  to unlock the load stopper  310 .  
         [0071]     Now referring to  FIG. 17 , a side view illustrates other interactive safety features between the load control and the engagement control in the first preferred embodiment according to the current invention. The isolated side view is seen from the side of the load carrying unit  200  as indicated by an arrow in  FIG. 7 . Certain components are not discussed here since the description has been already provided with respect to  FIG. 14 . As already described with respect to  FIG. 14 , the rotatable knob  292  at the position  292 A is in the engaged state, and the distal end  290 E of the vertical portion  290 A disengages itself from the bore  153 A of the bottom plate  153 . When the hook engagement control unit is in the engaged state, the operator is allowed to rotate the rotatable load lock handle assembly  320  as discussed with respect to  FIG. 16 . After the rotatable load lock handle assembly  320  is rotated to the predetermined load unlock position, the load control is in the disengaged state. The load stopper  310  is now unlocked so that a load can be delivered from or retrieved to the load carrying unit  200  as discussed with respect to  FIGS. 10 and 15 .  
         [0072]     Still referring to  FIG. 17 , the isolated side view illustrates the load control in the disengaged state in relation to the engagement control in the engaged state in the first preferred embodiment according to the current invention. After the rotatable load lock handle assembly  320  is rotated to the predetermined load unlock position, the shift block plate  340  is placed at the upright position  340 A adjacent to the linkage connecting plate  290 D behind the movable control lever  290 . At the predetermined load unlock position, the upright position  340 A prohibits the movable control lever  290  from moving in the backward direction. In other words, the operator is prevented from shifting the movable control lever  290  into the disengaged state to place the hooks  270  in the predetermined disengaged position while the load control is in the disengaged state. This mechanism automatically ascertains safety during the load delivery or retrieval by preventing the operator from accidentally disengaging the hooks  270 .  
         [0073]     Now referring to  FIG. 18 , a side view illustrates yet another interactive safety features between the load control and the engagement control in the first preferred embodiment according to the current invention. The isolated side view is seen from the side of the load carrying unit  200  as indicated by an arrow in  FIG. 7 . Certain components are not discussed here since the description has been already provided with respect to  FIG. 14 . As previously discussed with respect to  FIG. 16 , despite the presumption on the hook engagement, the additional safety feature forces the operator to retract the load control knob  320 A to the retracted position  320 A″ while rotating the rotatable load lock handle assembly  320  to a predetermined unlock position. This safety feature is further conditioned upon the position of the movable control lever  290  of the engagement control as will be described here.  
         [0074]     Still referring to  FIG. 18 , the side view illustrates the engagement control in the disengaged state to block the load control in the preferred embodiment according to the current invention. As previously described, the rotatable knob  292  rotates between the two positions  292 A and  292 C. At the position  292 C, the rotatable knob  292  is in the disengaged state for placing the hooks in the predetermined disengaged position and is locked by the urging from the spring  293 F so that the distal end  290 E of the vertical portion  290 A engages with a bore  153 A of a bottom plate  153 . At the position  292 C, since the movable control lever  290  has shifted from the front position  292 A to the backward position  292 C to rotate around the linkage  294  in the direction indicated by an arrow, the physical distance to the rotatable handle arm  320 G and the movable control lever  290  has been reduced.  
         [0075]     While the engagement control is in the disengaged state as shown in solid lines, when the operator attempts to rotate the rotatable load lock handle assembly  320  of the load control by retracting the load control knob  320 A to the retracted position  320 A″, yet additional safety feature blocks the rotation due to the reduced distance. Although the load control knob  320 A is retracted to the retracted position  320 A′, the terminal end  320 B-T of the safety pin  320 B at its retracted position  320 B-T′ still fails to clear the linkage connecting plate  290 D due to the reduced distance. In other words, the operator is not allowed to unlock the load unless the hooks are at the predetermined engaged position according to this safety feature.  
         [0076]     Now referring to  FIGS. 19A and 19B , a flow chart illustrates steps involved in a preferred process of operating the safety enhanced load carrying device according to the current invention. The acts or steps are described in relation to the components, units and mechanisms of the first preferred embodiment according to the current invention. Thus, the reference to these components in the first preferred embodiment is made with respect to  FIGS. 5 through 18 . In the preferred process, for example, a predetermined load M such as a battery is delivered to or retrieved from a desired destination structure such as a forklift  410  via the safety enhanced load carrying device of the current invention as shown in  FIG. 10 .  
         [0077]     Now referring to  FIG. 19A , in a step S 1 , the operator moves the safety enhanced load carrying device towards the predetermined destination. The operator attempts to engage the load carrying unit  200  with the predetermined structure in a step S 2 . As the load transporting unit  100  and the load carrying unit  200  approach the predetermined structure in the step S 1 , the guide pin  330  is aimed at the corresponding receiving structure  430  on the forklift  410  so that the appropriate engagement between the hooks  270  and the hook engagement unit  420  is attempted in the step S 2  as illustrated in  FIG. 10 . In a step S 3 , it is determined whether or not the appropriate engagement is successfully completed. If it is determined in the step S 3  that the engagement is successfully completed between the hooks  270  and the hook engagement unit  420 , the preferred process proceeds to a step S 5 . On the other hand, if it is determined in the step S 3  that the engagement is not successfully completed, it is ascertained in a step S 4  that the engagement control is in the engaged state. In other words, as described with respect to  FIG. 11 , in order to successfully conclude the hook engagement, the movable control lever  290  of the engagement control must be in the engaged state. Then, the preferred process proceeds back to the step S 2  to continue the engagement attempt as described above.  
         [0078]     Still referring to  FIG. 19A , the preferred process continues to accomplish the rest of the steps according to the current invention. Upon successfully completing the hook engagement, the operator attempts to unlock the load in the step S 5  by rotating the rotatable load lock handle assembly  320  of the load control while retracting the load control knob  320 A to the retracted position  320 A″. Here, unlocking the load does not necessarily mean that the load must exist in the load carrying surface  200 S. Rather, the same phrase is used to mean that the load block plate  310  is successfully released from the load carrying surface  200 S. The attempt is determined in a step S 6  whether or not the load block plate  310  is successfully released from the load carrying surface  200 S. If it is determined in the step S 6  that the load control is successfully placed in the load unlock state, the preferred process proceeds to a step S 8 . On the other hand, if it is determined in the step S 6  that the load control is not successfully placed in the load unlock state, the preferred process proceeds to a step S 7 , where the operator ascertains that the engagement control is in the engaged state. In other words, as described with respect to  FIG. 18 , if the movable control lever  290  of the engagement control is in the disengaged position, the linkage connecting plate  290 D prohibits the rotation of the rotatable load lock handle assembly  320  to the load unlock position. Following the step S 7 , the preferred process repeats the step S 5 .  
         [0079]     After confirming that the hooks  270  are engaged and the load block plate  310  is placed out of the load carrying surface  200 S, the predetermined task is performed. In a step S 8 , it is determined that the predetermined task is either delivery or retrieval of the load. If it is determined in the step S 8  that the predetermined task is a delivery task, a step S 9  is performed to deliver the load from the battery carrying surface  200 S of the load carrying unit  200  to a predetermined battery bay of the forklift  410 . On the other hand, if it is determined in the step S 8  that the predetermined task is a retrieval task, a step S 10  is performed to retrieved the battery from the predetermined battery bay of the forklift  410  onto the load carrying surface  200 S of the load carrying unit  200 . After performing the predetermined task, the preferred process now prepares for the disengagement as illustrated in  FIG. 19B .  
         [0080]     Now referring to  FIG. 19B , the flow chart illustrates steps that follow the above described predetermined task according to the current invention. It is determined in a step S 11  whether or not the preferred process has completed the predetermined retrieval or delivery task. If the step  11  determines that the predetermined task has not been completed, the preferred process waits at the step  11 . On the other hand, the predetermined task is completed, the preferred process proceeds to a step S 13 . For example, upon confirming the appropriate retrieving position M′ of the retrieved battery, the operator secures the battery pack M on the load carrying units  200  by rotating the rotatable handle  320  in the counterclockwise direction so that the load block plate  310  is placed at the front end of the load holding surface  200 S for blocking the forward movement of the battery pack M.  
         [0081]     Still referring to  FIG. 19B , the preferred process performs the steps associated with further safety according to the invention. The preferred process determines in a step S 14  whether or not the locking step S 13  is completed. If it is determined in the step S 14  that the locking step S 13  has not successfully completed, the preferred process goes back to the step S 13 , where the operator repeats the load locking task. However, if the step S 6  has been successfully completed, the shift block plate  340  of the load control is at the upright position behind the linkage connecting plate  290 D to prevent the movable control lever  290  of the engagement control from shifting backward into the disengaged state. For this reason, the load locking step S 13  should be always successfully determined in the step S 14 .  
         [0082]     After the successful load locking task in the S 14 , the operator is ready to disengage the hooks  270  from the forklift  410 . After successfully locking the load in the step S 14 , the operator attempts to shift the movable control lever  290  of the engagement control in the backward direction into the disengaged state in a step S 15 . It is determined in a step S 16  whether or not the disengagement task is successfully completed. If it is determined in the step S 16  that the disengaging step S 15  has not successfully completed, the preferred process goes back to the step S 15 , where the operator repeats the hook disengaging task. However, if the step S 13  has been successfully completed, the shift block plate  340  of the load control is placed away from the upright position behind the linkage connecting plate  290 D and no longer prevents the movable control lever  290  of the engagement control from shifting backward into the disengaged state. For this reason, the disengaging step S 15  should be always successfully determined in the step S 16 . Finally, the disengaged load carrying unit  200  with the load block plate  310  in the load lock position is moved away from the forklift  410  in a step S 17 . Then, the preferred process terminates.  
         [0083]     Lastly, referring to  FIG. 20 , a prospective view illustrates a second preferred embodiment of the safety enhanced load carrying device  600  according to the current invention. Generally, the load carrying portion is integrated with the load transporting portion by fixedly placing the load carrying portion on top of the load transporting portion. The front side of the load carrying portion having the hooks  270  and the guide pin  330  is placed on a far side away from the handle  160 . This is because this far side is placed near a predetermined structure so that the guide pin  330  will guide the safety enhanced load carrying device  600  to a predetermined structure. For example, the guide pin  330  will guide to a desired position by being inserted into a complementary hole on the predetermined structure. Unlike the first preferred embodiment, the second preferred embodiment lacks the height adjustment mechanism. Thus, the guide pin  330  maintains the same height with respect to the ground. As safety enhanced load carrying device  600  arrives the predetermined structure, the hooks  270  engage with a certain portion of the predetermined structure.  
         [0084]     The back side of the safety enhanced load carrying device  600  has the movable control  290  and the load control rotatable handle  320  near side of the handle  160  of the safety enhanced load carrying device  600 . This side is a control side which should be accessible to the operator, and the operator controls the moving direction of safety enhanced load carrying device by steering the handle  160  towards the desired structure via the front wheels  190 A and the rear wheels  190 B. Upon arriving at the desired structure, the rear wheels  190 B are locked to park the safety enhanced load carrying device  600 . The operator then controls the safety features such as the hook engagement by the movable control lever  290  and the load locking by the rotatable handle  320 . Since the operator is standing away from the moving load and has easy access to all of the controls, the safety is further promoted. The safety features of the second preferred embodiment are substantially identical to those of the first preferred embodiment except for the features associated with joining the load transporting unit  100  and the load carrying unit  200  of the first preferred embodiment. For this reason, the safety features of the second preferred embodiment are not reiterated for the movable control lever  290 , the rotatable handle  320 , the load block plate  310 , the shift block plate  340 , the linkage connecting plate  290 D, the hooks  270  and their interactions.  
         [0085]     The above description of the first and second embodiments is given for the mechanical implementation. However, some safety features of the current invention are implemented in an alternative embodiment using electronic components including microprocessors, sensors and or software to control the activation of the movement, timing and tracking the status  
         [0086]     It is to be understood, however, that even though numerous characteristics, features and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and that although changes may be made in detail, especially in matters of shape, size and arrangement of parts, as well as implementation of the control mechanism in software, hardware, or a combination of both, the changes are within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.