1.  Field of the Invention
The present invention relates, in general, to a storage system such as automatic warehouses designed to take a great quantity of goods or many vehicles into or take them out of storage spaces on storage forks of racks in order to allow users to effectively store and manage goods or vehicles and, more particularly, to a palletless loading structure for a storage system for quickly and safely taking goods into and/or taking them out of a storage space on storage forks free of additional support pallets. 
2.  Description of the Prior Art
As well known to those skilled in the art, storage systems are a facility designed to store goods or other materials in a limited storage place and manage the stored goods or materials, effectively, which has been widely used as part of a large-scale material flow system or a warehouse in other industrial work places. 
As shown in FIG.  1, a conventional storage system comprises a plurality of racks R having a vertical multistory configuration of a plurality of loading stages L, in which the racks R are arranged on a support surface spaced in an interval from each another to form a building structure and the loading stage L includes a movable support pallet (not shown) laid thereon to load goods, and a transporting unit T such as a lift or a stacker crane installed in an elevation space between the racks R to be vertically moved to put goods into or take goods out of a storage space on the loading stage L.
The transporting unit T carries a support pallet loaded with the goods W to an empty loading stage L of the rack R. Then, the goods-loaded support pallet is pulled over in a horizontal direction by a traction unit (not shown) to be placed onto the empty loading stage L and the goods shipment from the storage spaces vise versa. 
In the storage system, what is more important is the quick and accurate storage, shipment and inventory management of goods W. To it, the transporting unit T is under the control of a computer (not shown) to be automatically operated, so that goods W are automatically put into or taken out of the storage space on their loading stages L with particular inherent number or code being allotted to goods W and the loading stage L, respectively. 
However, the conventional storage system needs a plurality of support pallets and at least one traction unit, separately, for the storage and shipment, so its loading configuration becomes complex.  Further, a gross load imposed on the racks R as well as on the traction unit T during carrying goods W along with the support pallet is increased by a weight of a plurality of support pallets or one pallet and has to be reflected into the total configuration design of the storage system or the traction unit T. In case of the traction unit T, the support pallet has a bad effect on a power and time used up in carrying goods W.
If some goods-free or empty support pallets are placed on the loading stages S, it is necessary for the transporting unit T to remove the empty support pallet from the corresponding loading stage S in advance.  For example, the transporting unit T is moved to the loading stage S to pull out the empty support pallet therefrom for next goods storage and then to a carrying-in position to be on standby.  Otherwise, the traction unit T carries the empty support pallet to be put on another loading stage L, on which nothing is laid, according to a storage or shipment control signal before being moved along with the empty pallet to a standby position.  Thereafter, the transporting unit T performs the normal operation for the storage or shipment that target goods W is stored in a predetermined loading stage L or taken out of its loading stage L along with the corresponding support pallet.  For it, the conventional storage system has a disadvantage in that it takes much time in putting goods into or taking goods out of the storage spaces of the loading stages following by the separate dealing of the support pallet. 
In an effort to overcome the above-mentioned problems experienced in the conventional storage system using such support pallets, a palletless loading configuration without requiring support pallets in putting goods into or taking goods out of the storage spaces on loading stages has been proposed and used.  A typical example of such palletless loading structures is disclosed in International Laid-open Publication No.  WO 87/02405 entitled “Vertical Storage Apparatus and Control Method Thereof”. 
As shown in FIGS.  2A and 2B, the vertical storage apparatus comprises a single rack unit including an elevation space and multi-storied storage racks provided on at least one side out of the left side, right side, front side and rear side of the lift space.  The rack comprises a plurality of storage forks 1 normally arranged on every story thereof to form two rows spaced apart in a regular interval from each another.  The elevation space defined between the storage spaces comprises a pair of elevation forks 2 mounted to be moved up and down therein to carry goods W in a vertical direction.  The storage fork 1 reciprocates between a storage space and the elevation space by a drive unit (not shown) in a manner to be moved toward or away from a position above or under the fork bars of the elevation forks 2 according to the guidance of a horizontal guide beam 3 of the rack.  The elevation fork 2 comprises a pair of elevation forks 2a and 2b faced to each other, fork bars of which are vertically passed through between fork bars of the storage fork 1 to be placed at a loading/unloading position in the elevation space, without interfering with the fork bars of the storage fork 1.  In such a case, the paired forks 2a and 2b are synchronously moved. 
In a storage operation, the elevation fork 2 loaded with goods W on its fork bars are first moved upward in the elevation space to a desired position higher than that of a target empty storage fork 1.  The target empty storage fork 1 is horizontally moved inward into the elevation space by the drive unit to a loading position under the fork bars of the elevation fork 2.  The elevation fork 2 is moved downward to cross the fork bars of the storage fork 1 in order to load the goods W onto the storage fork 1.  The storage fork 1 with the goods W is returned by the drive unit to its original position, so that goods W is taken into a storage space of the rack. 
However, the vertical storage apparatus free of a pallet has a problem in that the moving distance of the elevation fork 2 is relatively longer, because the elevation fork 2 passes through or cross the storage fork 1, vertically, during a loading or unloading operation. 
That is, a target storage fork 1 must be horizontally moved to a loading or unloading position under or above an elevation fork 2 without causing any interference between goods W and any one of the storage and elevation forks 1 and 2.  Therefore, a substantial travel of the elevation fork 2 is a sum of adding operational allowance gaps “g1” and “g2” to two heights h1+h2 of the storage fork 1 and the elevation fork 2.  It takes a relative longer time for the storage and shipment of goods W, so that the vertical storage apparatus fails to reduce the time consumption during a loading or unloading operation. 
Another typical example of a loading structure for a storage system free of a pallet is referred to Japanese Patent Laid-open Publication No.  Heisei.  5-52058 entitled “Loading structure for stacker crane-type parking garages”. 
As shown in FIGS.  3A and 3B, a loading structure for a stacker crane-type parking lot comprises two racks 4 installed on a support surface to be spaced apart at an interval from each other and a stacker crane (not shown) mounted between the racks 4 to enable a lift fork 7 to be moved up and down with being loaded with goods W. Multiple cantilever support bars 6 are provided on the right and left shelf members of each rack 4 to form a storage space inside horizontal support beams 5.  The lift fork 7 includes a plurality of arm bars 9 provided on both sides of a body 8 of the stacker crane to cross the support bars 6 without any interference during being lifted or lowered in a protruded state. 
In a loading operation, the lift fork 7 loaded with goods W is first moved upward in an elevation space to a desired position higher than that of the support bar 6 and then horizontally to be entered into a target empty storage space of the racks 4.  Thereafter, the lift fork 7 is moved downward to cross the support bar 6 of the rack 4.  During the downward movement of the lift fork 7, the arm bars 9 pass through the spaces between the support bars 6 without any interference to load goods W onto the support bars 6.  The lift fork 7 is, thereafter, laterally moved from the position under the support bars 6 to a position inside the elevation space, prior to being moved to a standby position where another goods W are loaded on the lift fork 7. 
However, the loading structure is designed such that the lift fork 7 passes through the support bars 6 from above its upper portion to below its lower portion thereby to return to its original position, so it has a limitation to the time reduction in taking in or out of goods W due to a relatively longer traveling distance. 
Therefore, a substantial travel of the lift fork 7 is a sum of adding allowance gaps “g1” and “g2” for entering into/retracting from the rack 4 to two heights h3+h4 of the support fork 6 and the lift fork 7.  It has a limitation to the shortening of a vertical traveling distance of the lift fork 7. 
In addition, the support bars 6 are extended from both sides of the horizontal support beam 5 to a predetermined length to allow goods W to be placed thereon, because goods W has to have widths larger than that of a space defined between the support bars 6 in each storage space to be effectively stored on the support bars 6 without being dropped through the space.  It has a limitation to a size of goods W that can be stored in the storage system.