US 3070248 A
Description (OCR text may contain errors)
Dec. 25, 1962 E. MITCHELL 3,070,248
STRUCTURAL MEMBER FLEXIBLE IN A SINGLE DIRECTION Filed Nov. 9, 1959 2 Sheets-Sheet 1 r x k U W j w E/gin Mitchel/ ATTORNEY Dec. 25, 1962 MlTCHELL 3,070,248
STRUCTURAL MEMBER FLEXIBLE IN A SINGLE DIRECTION Filed Nov. 9, 1959 2 Sheets-Sheet 2 I INVENTOR.
. E Igin Mifchel/ ATTQRNEK,
3,070,248 STRUCTURAL MEMBER FLEXIBLE IN A SINGLE DIRECTION Elgin Mitchell, 904 Cottonwood Ave., Hayward, Calif. Filed Nov. 9, 1959, Ser. No. 851,778 9 Claims. (Cl. 214-731) The present invention relates to the construction of load supporting beams and more particularly to a flat member which is flexible in a first direction and capable of sustaining a load applied in the opposite direction.
The invention will be herein described with respect to usage in conjunction with fork-lift industrial trucks, whereby retractable blades are provided thereon, such usage being representative of the application of the invention. It should be understood, however, that the invention has diverse applications in other apparatus and structures, examples of which will be hereinafter pointed out.
In the handling, storage and shipping of many forms of goods it is particularly convenient to stack the goods on slightly raised platforms or pallets. The stack may then be lifted .as a unit by means of a fork lift truck for transporting or rearrangement. The widespread use of such pallets in conjunction with the lift trucks has effected a very considerable saving of labor and time in the handling of materials.
Fork lift trucks have been made in a variety of forms and sizes ranging from small hand driven units which elevate the load a few inches, in order that it may be rolled, to very large motorized machines with which the loads may be lifted a considerable distance and tiered vertically. All but a few specialized forms of such trucks have as a common feature a pair of spaced parallel blades which extend forwardly from the truck and which are inserted under the pallet and load and then elevated. With the load thus supported, the truck may be moved as desired and the load may be subsequently deposited at a desired point by lowering and withdrawing the blades.
It is also a common characteristic of lift trucks as heretofore constructed that the distance which the blades extend forward from the body of the truck is fixed. The length of the blades must be considerable in order to carry a suflicient bulk and to provide for the support of maximum weight, and it has been the practice to use solid inflexible material to form the blades. The forward extension of the rigid blades, however, creates several very significant problems in the use of such trucks.
A first difliculty associated with the use of rigid fixed blades is the considerable area which must be set aside for maneuvering the truck. In a warehouse, or other storage area, it is generally desirable that a maximum quantity of goods be stored in a minimum area. The width of the aisles which must be left between adjacent rows of goods is determined by the length of the truck and blades and by the requirement that the truck must be able to turn at right angles to the aisle to pick up and deposit material. Thus the long blades result in a very appreciable loss of potential storage space.
Related to the foregoing problem is the consideration that a truck with fixed blades must be made sufliciently long to handle the maximum anticipated load. If a single truck is to handle pallets of two different sizes, the blades must be long enough to accommodate the larger size and a large maneuvering space is needed even where the smaller pallets are stored. Thus it may be seen that considerable savings in storage space may be realized if the blades are made retractable and can be extended only as far as is necessary to handle any particular load.
A second problem arising from the use of rigid fixed blades on a lift truck is that of safety. When the truck is unloaded the blades are generally carried in a low posi- States P tion and are therefore somewhat out of the normal line of view of both the operator and bystanders. In addition many forms of truck have a bulky load hoisting structure that further impedes the operators view in the forward direction. These circumstances contribute to accidents and in view of the narrow projecting configuration of the blades such accidents are frequently serious.
In addition to the personnel hazard, the blades can easily catch on stored material and topple a stack of goods, the problem being aggravated by the restricted spaces in which the trucks must frequently be operated. Such collisions may damage the goods or other nearby equipment and, if severe, may bend the blades to the point where .a load may not balance evenly thereon.
To overcome the foregoing problems, the present invention provides a novel blade construction, together with guiding means and controlling means, which can be retracted when unloaded and which can be extended only as far as is necessary to handle a particular load. Specifically, the invention uses a blade formed of a series of links pivoted together in a unique fashion sothat the structure may be fiexed in one direction but which cannot bend in the opposite direction. Owing to this unidirectional flexibility, the blades may be withdrawn towards the truck and caused to turn upwardly into vertical guides secured to the forward face of the truck. While such retraction and extension of the blades may be conveniently done manually on smaller trucks, the system is readily adapted to control by power driven means such as pneumatic or hydraulic cylinders, chain drives, an electrical motor, or other.
The blades are made capable of flexing in the upward direction, while being able to support a normal load without bending in the downward direction, by forming the blades from a series of rectangular platforms disposed end to end and connected together by pivoting braces. Specifically, each platform is formed with a number of parallel grooves which grooves run lengthwise along the upper surface thereof. Each adjacent pair of the platforms are interconnected by a pair of linear brace members. Each of the brace members which straddles a neighboring pair of platforms lies along a groove of the platforms and enters the grooves when the blade is straightened. The two ends of each brace member are pivotably attached to the two platforms by transverse pins which extend across the grooves.
The structure may easily bend in the upward direction since the brace members may rise out of the grooves allowing each platform to be inclined with respect to the following one. No such flexing can occur in the downward direction inasmuch as the brace members then bear against the bottom of the grooves and, in effect, splint the structure to form a rigid beam.
Considering now a further feature of the structure which acts to maximize the load sustaining capabilities of the blade and to insure rigidity thereof, the brace members are preferably made considerably longer than the mini-mum distance required to connect two adjacent platforms, the braces being pivotably attached to each of the two adjacent platforms at points distant from the boundary therebetween. Preferably the length of the braces should be such that the two sets of braces on each platform, which connect with the two neighboring platforms, overlap for a substantial portion of the length of the platform, the two sets of braces being laterally offset from each other to avoid interference. Using this construction, the stress which must be sustained by the structure is distributed rather than being concentrated as would be the case if simple pivot joints were used at the boundaries between adjacent platforms. Thus the structure need not be of unduly massive construction and the effect of such factors as elasticity is minimized.
It is thus an object of this invention to provide a structural element which may be flexed in one direction and which resists flexure in the opposite direction.
It is an object of the invention to provide a flat structural member which may be cantilevered and used to support a load, the member being flexible in a direction opposite to that at which said load is applied.
It is a further object of this invention to provide a load supporting member which is flexible in one direction only and in which the stress from a load is distributed along the member whereby component parts thereof need not be of massive construction.
It is an object of the invention to provide a retractable load sustaining structural element which may retract at right angles to the normal position thereof.
It is still another object of this invention to provide a retractable blade construction for an industrial truck.
It is an object of the invention to provide a blade construction for a fork-lift truck whereby the blades may be retracted and may be extended only as far as is necessary to handle a particular load.
It is a further object of the invention to reduce the free space required for maneuvering industrial trucks whereby a more complete utilization of warehouse space may be accomplished.
It is still a further object of this invention to decrease the likelihood of personnel accidents and damage to goods in connection with the operation of fork-lift trucks.
The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the accompanying drawing, in which:
FIGURE 1 is a perspective view of a structural element which is flexible in a single direction only, the element being shown in the flexed position,
FIGURE 2 is a perspective view of the structural element of FIGURE 1 shown in the linear position,
FIGURE 3 is a cross section view of the structural element taken along line 3-3 of FIGURE 2 and illustrating the mode of coupling of component members thereof,
FIGURE 4 is a section view taken along line 4-4 of FIGURE 3 and further illustrating the structure shown therein, and
FIGURE 5 is a perspective view showing the utilization of the structural element of FIGURES 1 to 4 as retractable biades on a fork-lift industrial truck and showing suitable drive mechanism for controlling the movement of the blades.
Referring now to the drawing and more particularly to FIGURES l and 2 thereof, the structural element is comprised of a series of flat rectangular platform members 11 disposed end to end to form a column thereof. The number of platforms 11 which are utilized and the length of each one thereof may be varied according to the length which the assembly is to span and according to the degree of flexibility required but in general it will be found advantageous to make the platforms with the maximum length which is consistent with the desired flexibility and to make the platforms of identical size and configuration so that additional units may be attached if desired.
The surface of each platform 11 towards which the assembly is to be flexible, in this instance the upper surface 12, is provided with a number of longitudinal grooves 13 of rectangular cross-section. Preferably the grooves 13 of successive ones of the platforms 11 are in alignment and since each neighboring pair of platforms in this embodiment is to be linked by a pair of braces, the grooves are four in number in the example shown. To provide for the installation of pivot pins as will hereinafter be described, each of the platforms 11 is transpierced by a pair of spaced apart bores 14 which bores are parallel to upper surface 12 and which intersect the grooves 13. The 'bores 14 should be separated a substantial distance and in this instance are situated one third of the length of the platform 11 inward from each end thereof.
Each of the plaforms 11 is linked with each adjacent platform by a pair of linear braces 16, the braces having a width conforming to that of the grooves 13 so that the braces may enter into the grooves. To provide the assembly with maximum strength when in the linear position, the braces 16 should be made long in relation to the length of the platform 11 but should not exceed twice the length thereof if the platforms are to be adjacent when the assembly is straightened. The length of the braces is interdependent with the position of bores 14 on the platforms and thus in this instance the braces exceed the length of the platforms 11 by slightly in excess of one third the length thereof, the slight excess being required since the ends of the braces must extend slightly beyond the bores and since a slight gap 17 must be present between each neighboring pair of platforms to allow one to be inclined with respect to the other.
With the assembly in the linear position as shown in FIGURE 2, each brace 16 lies along a groove 13 and straddles the boundary between a neighboring pair of the platforms 11, the brace extending along two-thirds of the length of each of the platforms. Each of the pair of braces 16 connecting a pair of neighboring platforms 11 occupies a separate groove 13, the pairs of braces alternately occupying the two outermost grooves and the two innermost grooves with respect to successive sets of adj acent platforms.
Referring now to FIGURES 3 and 4, the mode of pivotably attaching the ends of the braces 16 to the platforms 11 is shown. Such connection, in this embodiment, is made by a traverse pivot pin 18 disposed in the platform bores 14 and transpierced through matching bores 19 in the ends of the braces. As shown in FIGURE 3 in particular, a single length of pivot pin 18 may be used to cross both of the innermost grooves 14, the pin being terminated short of the outermost grooves since the outermost braces 16 must be able to enter therein. The pin 18 is here shown secured in place by a weld 21 to form a permanent assembly it being understood that other forms of fastening, such as set screws or threaded fatsenings, may be employed if a unit which may be varied in length is desired.
As shown in FIGURE 4 in particular, the elevation of bore 14 from the bottom surface 22 of groove 14 is related to the height of the brace 16 so that the brace lies against surface 22 when the assembly is straightened, the braces thus effectively splinting the assembly against flexure in the downward direction. To permit relative movement between the braces 16 and platforms 11 in the upward direction, however, the end 23 of the brace is rounded.
In operation, and with reference to FIGURES 1 and 2, it may be seen that the structure is bendable in the upward direction and may be coiled in this direction in a close approximation of a smooth curve. Such action results from the fact that the platforms 11 are pivotably attached to the braces 16 which braces may in turn be inclined with respect to each other. In contrast, the structure cannot bend downwardly from the straightened position inasmuch as the platforms 11 cannot pivot in this direction about the ends of the braces 16. Considering now a highly advantageous property of the structure from the standpoint of rigidity and strength, the fact that the braces 16 are made long relative to the platforms 11, and overlap along the upper surface of the assembly, results in a distribution of stress along the assembly and allows a very considerable downwardly directed load to be supported without requiring that the elements of the assembly be of massive construction as would be the case where stress is concentrated around pivot points.
The foregoing structure is highly advantageous in a wide variety of applications. The construction is useful, for example, in the design of doors, gates, and the like where space considerations require that the door or gate must be retractable at right angles to the normal position. The construction may be used to provide a conveyor belt capable of carrying a much greater weight than the fabric belts heretofore employed, and the application of the construction to collapsible architectural structures will be apparent.
Referring now to FIGURE 5, a highly advantageous use of the structure is illustrated, specifically use in a retractable blade construction for a fork-lift truck. Considering first such conventional features of the truck as are necessary to relate the present invention thereto, there is shown a truck body 24 mounted on wheels 26 and provided with an operators seat 27. At the forward face of body 24, two upright spaced apart channel posts 28 are provided, the facing sides of which posts each have a pair of longitudinal grooves 2-9. To provide additional support for the posts 28, a cross-piece 31 extends between the posts at the lower end thereof and flat cross braces 32 extend between the members at spaced points therealong.
A flat rectangular upright faceplate 33 is adapted to travel in the vertical direction along the posts 28, the faceplate being positioned slightly forward from the posts and having transverse rods 34 secured to the rearward edge by means of clamps 36. The ends of rods 34 enter the more forward grooves 29 of each post 28 and a roller wheel 37 is mounted on each rod end to hold the faceplate 33 against the posts while permitting it to he traveled upwardly and downwardly for the purpose of elevating or depositing a load.
To provide for, and control, vertical motion of the faceplate 33, various mechanisms may be used, the present embodiment being provided with a hydraulic drive cylinder 38 which cylinder is upright and secured to crossbraces 32 at a position midway between the posts 28. The extensible drive shaft 39 of cylinder 38 is directed upwardly and is connected to a transverse rod 41 which rod extends between the more rearward grooves 29 of the posts 28. To prevent rotation of cylinder drive shaft 39 and to reduce friction in the mechanism, a roller wheel 42 is mounted on each end of the rod 41 which wheels ride in the grooves 29. A pair of sprocket wheels 43 are rotatably mounted on rod 41, one on each side of drive shaft 39. To couple motion of the drive cylinder shaft 39 to faceplate 33, a pair of chains 44 are employed, each having one end secured to a cross brace 32, at the level of the upper end of the drive cylinder, by clamp plates 46. Each of the chains 44 extend upwardly around a separate one of the sprockets 43 and then extend downwardly, the second ends of the chains being secured to the rearward surface of faceplate 33 near the lower edge thereof.
Extension of the drive cylinder shaft 39 will thus act to elevate the faceplate 33, the distance traveled by the faceplate being twice that traveled by the cylinder drive shaft. To effect and regulate this motion, a suitable source of high pressure fluid must be provided within the truck body which source is connected to the cylinder 38 through a control valve situated within the reach of the operator. Inasmuch as such mechanism is conventional and well understood by those skilled in the art, the detailed structure thereof need not be described herein.
In the conventional practice, the fork-lift truck is provided with a pair of spaced horizontal rigid blades secured to the forward surface of faceplate 33, the structure being subject to the disadvantages hereinbefore discussed. Considering now the novel provisions of the present invention whereby retractable blades are provided for, there is shown a pair of vertical blade guide channels 47 secured to the forward surface of the faceplate 33, the channels being spaced apart a distance equal to the desired spacing of the blades. The forward faces of the channels 47 are open except for the lateral margins thereof at which narrow lips 48 are provided. The lower portion 49 of each channel 47 is curved forwardly through substantially ninety degrees of arc and, for reasons to be hereinafter discussed, the center of curvature of the forward surface of the channel is displaced from the center of curvature of the rearward surface thereof so that the channel increases in depth towards the center of the armate portion thereof.
A pair of blade assemblies 51 are provided, one being slidably entered in each of the guide channels 47. The blade assemblies 51 are similar to the structure hereinbefore described with reference to FIGURES 1 to 4, and are thus comprised of platforms 11 disposed end to end and linked together by braces 16 distributed along the upper surfaces thereof. As has been described, the assemblies 51 are flexible in the upward direction only and thus may be entered in the guide channels 47 and slid there-in around the arcuate lower portions 49 into an upright position. In connection with such motion it will be noted that the open forward faces of the channels 47 allow the braces 16 to rise from the platforms as is necessary to accomplish flexing of the assemblies 51 and further the expanded depth of the channels at the curved portions 49 thereof allow the rigid linear platforms 11 to travel around the curve.
The blade assemblies 51 may thus be retracted into the channels 47 or projected outwardly from the face plate 33 to function as blades for the lift-truck. Provided extension of the blade assembly 51 does not exceed a distance where at least one of the platforms 11 together with a small portion of the adjacent platform remains in the channel 47, the blades cannot flex downwardly and may be used to lift and support a loaded pallet in the conventional manner. To provide a mash plate to steady the load, a flat rectangular plate 52 is disposed forwardly from plate 33, the two plates being parallel and spaced apart a distance equal to the forward extension of the curved lower portions 49 of the channels 47 and being secured together by members 53 which extend between the lateral edges of the two plates.
While in small trucks, the extension and retraction of the blade assemblies 51 may be accomplished manually, it will be found preferable, particularly in the case of large trucks such as that herein described, to provide a power drive means for controlling such movement. As one suitable drive mechanism, there is shown a second hydraulic drive cylinder 54 secured between plates 33 and 52 in an upright position, the cylinder being powered and controlled by an operator in a manner similar to drive cylinder 38. Cylinder 54 has a stroke length equal to one-half the desired travel of the blade assemblies 51 and is situated midway between the channels 47 at the elevation of the upper half thereof. The cylinder 54 is double acting and of the class having a reciprocable drive rod 56 which projects from both ends of the cylinder. At each end of the drive rod a short cross-piece 57 is secured, suitable bracing 55 being provided at the juncture between the members.
A sprocket wheel 58 is rotatably mounted on each end of cross-piece 57 and one of a pair of continuous chains 59 extends between the upper and lower sprocket wheels at each side of the cylinder 54. The rearmost length of each chain 59 is secured to the truck faceplate 33 by clamp plates 60, at an elevation corresponding to the central portion of the cylinder 54, so that as the cylinder drive rod 56 is traveled upwardly or downwardly the forward length of the chains must travel at twice the rate and will travel twice the distance covered by the drive rod.
A sliding cross-bar 61 extends between the forward faces of the guide channels 47, the cross-bar being held in place by roller wheels 62 secured to the ends of the crossbar in parallel relationship therewith, the roller wheels being engaged in vertical channel shaped guides 63 which extend along the outer lateral faces of the chan- 7 nels 47. The crossbar 61 extends behind the forward lengths of the chains 59 and is secured thereto by clamps 64 so that the crossbar is constrained to move with the chains and thus to move upwardly or downwardly along the guide channels 47 is accordance with the motion of drive cylinder rod 56 and at twice the rate thereof.
The rearward ends of blade assemblies 51 are secured to the crossbar 61 by bolts 66, the connection being made with some play between the assemblies 51 and the bolts inasmuch as the end platform 11 of the blade assembly must incline with respect to the crossbar at the lower limit of travel thereof. Thus the vertical movement of the crossbar is transmitted to the blade assemblies 51 and the blades may alternately be retracted into the guide channels 47 and extended forwardly therefrom for a selected distance.
It should be understood that the retractable blade construction is equally applicable to the diverse other forms of industrial trucks which are manufactured, the folk-lift truck herein described being but a representative example of the use of the invention. Similarly, other forms of power drive may be used for extending and retracting the blades, pneumatic drive cylinders, electrical motor drives, and mechanical coupling with the primary truck motor through a suitable clutch mechanism being examples of alternate power drives. It will be apparent that the blade movement may also be controlled by a manually turned handwheel disposed adjacent to the operators position and connected with the blades by a suitable linkage.
Thus while the invention has been disclosed with respect to a single preferred embodiment, it will be apparent to those skilled in the art that numerous variations and modifications may be made within the spirit and scope of the invention and it is not intended to limit the invention except as defined in the following claims.
What is claimed is:
1. In a structural member for sustaining a load applied in a first direction, said member being flexible in a second and opposite direction, the combination comprising a plurality of platform elements disposed end to end in a column and each having a substantially flat surface at the load sustaining surface of said column, and a plurality of substantially linear braces distributed along said column of platforms at said load sustaining surface thereof, said braces being separate from said platforms and at least one of said braces extending from each platform along a substantial portion of each platform adjacent thereto, the ends of each of said braces being pivotably connected to neighboring ones of said platform elements whereby said braces may pivot in planes at right angles to said flat surfaces.
2. In a normally linear load-supporting beam, flexible in a single direction, the combination comprising a plurality of platform elements positioned end to end and forming a column, a plurality of substantially linear braces distributed along said column on the load bearing face, thereof, said braces being separate from said platforms and having a length greater than that of said platforms and at least one of said braces being positioned to straddle the boundary between each neighboring pair of said platforms and extending along each of said neighboring platforms a distance exceeding one-half of the length thereof whereby said braces overlap along said column, and a plurality of pivot fasteners attaching the ends of said braces to said platforms.
3. In a load sustaining normally linear structural member, which member is flexible in a direction opposite to that in which said load is applied, the combination comprising a plurality of platforms disposed end to end to form a column and each having at least one longitudinal groove on the load sustaining face of said column, said grooves of neighboring ones of said platforms being in alignment, a plurality of substantially linear braces distributed along said column of platforms at said load sustaining face thereof, at least one of said braces straddling each neighboring pair of said platforms and having an end entered into the groove of each of said neighboring platforms, and a plurality of pivot axles extending across said grooves of said platforms and transpierced through said ends of said braces whereby said platforms are pivotably attached to said braces and whereby said braces enter said grooves when said member is in the linear position.
4. A load sustaining normally linear structural member substantially as described in claim 3 wherein said braces have a length exceeding that of said platforms and wherein the braces attached to each of said platforms which extend in opposite directions therefrom are overlapped for a distance along said platform.
5. In a normally linear structural element, which element is bendable in a single direction, the combination comprising a plurality of platform elements disposed end to end to form a column, said platforms having substantially fiat surfaces along the load bearing face of said column and having a plurality of parallel longitudinal grooves in said flat surfaces, a plurality of linear braces distributed along said face of said column of platforms, at least a pair of said braces extending across the boundary between each platform and a neighboring platform with the ends of said braces being entered in the grooves of said platforms, said braces having a length exceeding that of said platforms whereby said braces overlap along said face of said column of platforms, and a plurality of pivot pins extending across said grooves of said platforms and transpiercing said ends of said braces whereby said platforms are pivotally secured thereto.
6. A normally linear structural element substantially as described in claim 5 wherein said platforms are of rectangular configuration and wherein said platforms have a length exceeding one-half the length of said braces whereby said structural element forms a substantially solid rectangular beam when in the linear position.
7. A load supporting normally linear structural beam, flexible in a single direction, comprising a plurality of platforms positioned end to end to form a column, a plurality of braces disposed along the load supporting face of said column of platforms, said braces being separate from said platforms and being distributed along said column with at least a pair of said braces straddling the junction between each platform and the neighboring platform, said braces having a length exceeding that of said platforms and less than twice the length thereof whereby said pairs of braces overlap along said column, and a plurality of pivot axles secured to said platforms, said pivot axles being transverse to said column of platforms and being transpierced through the ends of said braces whereby said platforms are pivotally attached to said braces.
8. In combination with an industrial truck, a retractable load carrying blade construction comprising an upwardly directed guide channel secured against the forward face of said truck said guide channel having a lower por tion curved forwardly from said truck with the central forward face of said guide channel being open along the curved portion thereof, and a blade slidably entered in said guide channel, said blade being formed of a plurality of platforms disposed end to end in a column and linked together by a plurality of longitudinal braces distributed along the upper surface of said column and straddling adjacent pairs of said platforms, said braces having a length substantially exceeding that of said platforms and being separate therefrom with the ends of said braces being pivotally attached to said platforms whereby said blade may flex upwardly to enter said guide channel but is rigid with respect to a downwardly applied load.
9. In a fork-lift truck of the class having two forwardly projecting parallel blades for supporting a load, a retractable blade construction comprising a pair of spaced apart vertical guide channels secured to the forward face of said truck, said guide channels having the lower portions thereof curved forwardly, a pair of blade assemblies one being slidably entered in each of said guide channels, each of said blades comprising a plurality of substantially rectangular platforms disposed end to end to form a column with each platform having a plurality of longitudinal grooves on the upper surface thereof, said platforms being linked together by a plurality of longitudinal braces distributed along the upper surface of said column, at least a pair of said braces extending across the boundary between each adjacent pair of said platforms with the ends of said braces being entered in said grooves and attached therein by transverse pivot pins whereby said braces lie along said grooves when said blades are extended from said truck and said blades form substan tially solid rectangular beams and whereby said column References Cited in the file of this patent UNITED STATES PATENTS 138,304 White Apr. 29, 1873 2,574,045 Lapham Nov. 6, 1951 2,628,734 Jannsen Feb. 17, 1953 2,643,745 Olszewski June 30, 1953 2,819,811 Quayle Jan. 14, 1954 2,844,232 Le Roy July 22, 1958