US2621821A - Apron construction for fork lift trucks - Google Patents

Description

Dec. 16, 1952 "r. N. MELIN 2,521,821

APRON CONSTRUCTION FOR FORK LIFT TRUCKS Filed Nov. 1, 1948 a Sheets-Sheet 1 IN V EN TOR.

ZZ'OMAS M MEL/N,

W Y@ 4770 Eva.

Dec. 116, 1952 T. N. MELIN 2,621,321

APRON CONSTRUCTION FOR FORK LIFT TRUCKS Filed Nov. 1, 1948 3 Sheets-Sheet 2 UIIIIIIV' J 2" IN VEN TOR. fig? fi o/14,45 JV: MEL/N,

I zrrz/vsvs.

- 1952: 'r. N. M;E L.IN 2,621,821

APRON CONSTRUCTION FOR FORK LIFT TRUCKS Filed Nv.,i, 1948 3 Sheets-Sheet 5 INVENTOR.

Il /OM MMEL/N,

-WY@ Mi 197'?- @NEYS.

Patented Dec. 16, 1952 APRO'N CONSTRUCTION FOR FORK LIFT TRUCKS Thomas N. Melin, Los Angeles, Calif.

Application November 1, 1948, Serial No. 57,737

7 Claims.

The present invention relates generally to lift trucks of the various types widely used in industrial work for elevating and carrying loads in warehouses, storage yards, and the like, and is more particularly concerned with improvements in the load carrying mechanism of trucks of this character.

Industrial lift-type trucks of the character referred to herein, generally fall into either one of two principal categories according to the type of load handling mechanism employed on the truck. One chief type of load handling mechanism is the so-called "ram type in which a rigid bar or ram is attached to the forward end of the truck body and is adapted to be inserted into the hollow of a bulk load, as for example a plurality of automobile tires, or spools or rolls of wire or strip steel. The other chief type of load handling mechanism is generally designated as the fork type and comprises one or more forwardly extending members which form a platform upon which the load rests. The fork is adapted to be placed underneath the load, rather than into a hollow within the load; but in either the ram type or fork type lift, the load engaging member is first advanced relative to the load, and then is raised upwardly to lift and carry the load, the procedure being reversed to deposit the load at any desired point. Less frequently encountered types are trucks with a crane boom or with grippers in place of a ram or forks.

The present invention has been designed for particular use with fork type lift trucks, and has a particular application in the lumber industry where the size and physical characteristics of the loads create special problems. For these reasons. I show and describe this particular embodiment of my invention, and explain its advantages as it relates to handling and stacking lumber; but it will be understood that my invention is not necessarily limited thereto. My invention is obviously not limited to any particular type of load carried on or by the truck; and it will be apparent from the further description that the invention is also applicable to other types of trucks, if desired.

In handling lumber in lumber yards and the like, the loads are generally characterized by their relatively great bulkiness, and particularly by their length as it is quite common practice to handle loads of boards or timbers up to 24 feet long. In stacking loads of lumber, it is essential to obtain vertical alignment between the existing stack and the new load superimposed thereon, or in relation to warehouse walls or 2 fixed bearings on the ground, etc. When loads are of the same width, alignment is obtained by vertically aligning the front vertical face of the load with the face of the stack, or with some other face or object. Lumber is ordinarily stacked to around 20 to 22rfeet high, according to the ability of the lift truck. A stack this high must be steady and well balanced in order to be safe and not present a hazard to life and property; and if proper alignment of superimposed loads cannot be easily obtained in confined areas then the safe height of the stack is correspondingly reduced. This means less efficient use of a given quantity of yard space or an increase in the yard space required to stack a given amount of lumber.

The problem of properly stacking one load on top of another arises of course with all kinds of materials and loads, but some of these problems are particularly accentuated when handling lumber. Since lumber yards are ordinarily in the open, the stacks may be higher than in a covered warehouse where a ceiling or roof trusses ordinarily restrict the height of a possible stack considerably less than 20 feet. Also, most other loads are considerably shorter in their maximum horizontal dimensions than are long pieces of lumber. These conditions combine to make accuracy of vertical alignment in stacking boxes or the like of less importance and of less effect than when stacking relatively long loads of lumber. For example, if a load of 24 foot timbers is twisted around a vertical axis but one degree with respect to a pile of timbers upon which the load is to be set, the ends of the loads are displaced approximately 2 /2 inches horizontally from the forward face of the pile even though perfect alignment is obtained at the center. With a box or the like having a length of 5 feet, this horizontal oifset is reduced to the order of onehalf inch and may therefore be negligible. Thus it will be seen that the problem of obtaining vertical alignment of a load with the pile upon which the load is deposited becomes so aggravated and accentuated when handling lumber as to be, in fact, new in kind.

When the forks are immovable with respect to the truck frame or body, the truck as a whole must be moved in order to change the position of the load, even though it is desired only to rotate the load slightly in a horizontal plane. Even with an experienced operator this may re quire considerable backing and turning with a truck, all of which takes time, more physical labor, increases tire wear, and ties up expensive equipment so that the overall cost of handling and stacking the lumber is correspondingly increased. Even experienced operators of lift trucks find it extremely difficult to judge proper vertical alignment of the loads before depositing them because their position on the truck is such that they do not have the proper view or perspective to gauge alignment until the load is nearly in position to be stacked relative to other loads or warehouse walls. This is especially true if a given load is not at right angles to the load forks, and hence not at right angles to truck axis.

If it were possible for the truck operatorto make a straight run at a pile with the truck, these problems would not be so acute; but this is not possible ordinarily. A truck moves along aisles between stacks of lumber and must make a sharp turn in cramped quarters to come into position either to pick up or drop a load. Because of the size of the load, the truck has much less room to maneuver when it is carryinga load and moves in to drop'it. These factors place a premium on experienced truck operators; but even with a great amount of practice operators are still required to use a disproportionately large amount of time in obtaining proper align ment as compared with the time involved in transporting the load and in other operations.

These same considerations prevail when a lift truck is used for loading an ordinary type of truck that transports the lumber to a building site. Exact placement of the load on the truck is required in order to obtain the necessary balance on the truck for unloading. To facilitate load ing trucks, ithas been found helpful to provide the forks with an overhang or offset so that they can be moved out over the truck bed when loading into it.

Hence it becomes a general object of my invention to provide an improved load handling mechanism for lift trucks which is adapted to facilitate exact vertical alignment of the load with a similar pile or other object on which the load is to be placed.

It is also an object of my invention to provide a load engaging mechanism for an industrial truck which is capable of limited controlled movement in a horizontal plane independently of the truck movement.

It is a further object to provide a loadengaging mechanism for an industrial truck of such character that the maneuverability of the truck itself is improved and is such as to allow the truck to swing its forks in the same direction as its wheels when negotiating sharp corners, thus allowing the truck to operate effectively in smaller spaces than heretofore. This results in greater effectiveness and'efficiency from the truck, and in some cases better utilization of the yard space available for stacking.

It is a further object of my invention to provide a load handling mechanism for a truck of the character described having power controlled means for moving the load without moving the truck as a whole, thus enabling the operator to obtain accurate final movement of the loadwithout the necessity of moving the entire truck. Not only does this improve the accuracy of load place ment but it results in considerable savings of time and machine and tire wear, both when picking up a load and depositing it.

These objects and advantages of my invention are attained in the conventional type of lifttruck having a frame carrying an upright track along which anelevator means travels, by pivotally connecting load engaging means to the elevator means and providing power drive means by which the truck operator can produce and control movement of the load engaging means in dependently of the truck. Since it is normally desired to swing the load in a horizontal plane, the axis of the interconnecting pivot is vertical, or substantially so. In order to produce a minimum of lateral movement of the load, the vertical axis is placed as close as practical to the forward face of the fork base. Usually the load is against this face so that the face acts to position the load on the forks, and in this case the vertical axis substantially coincides with the adjoining or rear edge of the load itself.

Various types of power drive means may be used. Typically it may include a lead screw driven by an electric motor and in turn moving a travelling block laterally of the elevator. A lever pivotally connected to the travelling block and attached to the load engaging means causes the latter to swing when the block moves. Hydraulic means may be used to move the travelling block or its equivalent instead of the motor.

How the above objects and advantages of my invention, as well as others not specifically mentioned herein, are attained will be more readily understood by reference to the following description and to the annexed drawings, in which:

Fig. 1 is a side elevation of a conventional type of industrial lift truck showing the application thereto of my invention;

Fig. 2 is a fragmentary plan and section on line 2-2 of 1, but enlarged;

ig. 3 is a fragmentary vertical section on line 3-3 of Fig. 2;

Fig. 4 is an exploded isometric view of the major parts of the load handling mechanism;

Fig. 5 is a plan view of an industrial lift truck with load handling mechanism constructed according to my invention showing how the loac may be quickly and accurately oriented to attain exact vertical alignment with a stack; and

Fig. 6 is a fragmentary plan and section similar to Fig. 2 but showing a modified form of power control means.

There is shown in Fig. l a conventional type of fork lift truck to which my invention has been applied, this type of truck being one manufactured by the Hyster Company of Peoria, Illinois. This particular lift truck is typical of the various ones to which my invention can be applied and is illustrated here solely for the purpose of making a full disclosure of my invention; and it is to be understood that my invention is not necessarily limited to this particular make or type lift truck.

The lift truck comprises a frame of conventional characteristics, generally indicated at 10 and not shown in detail in the drawings, which carries the wheels that make the truck mobile. Forwardly disposed wheels l! are non-dirigible while the rearwardly disposed wheels 52 are dirigible. The frame also carries a power plant which serves as a source of power for moving the truck and hoisting the loads. This power plant is enclosed within hood l4 and comprises a suitable type of internal combustion engine. in some industrial trucks, particularly the smaller sizes, the power plant may include an 01 ric motor as a prime mover which is energized by storage batteries. A seat i3 is provided upon which the truck operator sits, facing forwardly, within reach of the various controls for operating the truck.

At theforward end of the truck are a pair of spaced, telescopic uprights I5 which are connected at their upper ends by a cross bar l6 (see Fig. 5). Uprights l5 form an upwardly ex tending track which guides the load handling mechanism, indicated generally at I8, as the load is lifted or deposited. The means for raising and lowering the load handling mechanism is illustrated herein only in a general fashion, since its details constitute no essential part of. the present invention; but this mechanism includes a centrally disposed hydraulic hoist 20 which rests at its lower end upon the truck frame and at its upper end bears against cross bar l6. Hoist 23 is operated by means of hydraulic fluid under pressure from a pump, not shown, which serves to raise and lower the hoist in a conventional and well known manner, the hoist in turn raisingand lowering the load handling mechanism I8. A typical raised position is shown in dot-dash lines in Fig. 1.

Uprights [5 are pivotally connected to frame ID by means of two short transversely extending stub shafts 2| journaled in two forwardly extending frame members 22. Shafts 2| are each attached at one end to one of uprights I5. This construction permits the uprights to be tilted forwardly or backwardly to a limited extent in a vertically extending plane, this tilting action being obtained by means of tilting assembly members 24 and 25.

There have been omitted from the drawings the details of the driving means for the truck wheels, the steering mechanism, the hydraulic system for operating the tilting assembly, and various other conventional elements which are considered unessential to the present invention,

, in order to simplify the drawings and thej jdismechanism in their up and down movement.

Bracket 33 carries a pair of forwardly extending arms 35 which engage and are fastened to the under side of the top transverse member 28g, to support the elevator and connect it to ..the bracket. The lower transverse member 2817 of the elevator is attached to bracket 33 by a pair of gusset plates 32, one at each side.

Engagement between the offset and elevator is maintained by a pair of bolts 35 which are slidably mounted in elevator 28, the arms 35 receiving the inner ends of bolts 36. Spaced lugs 290 are placed on the back side of offset 23, a pair of lugs being positioned at each side thereof to engage each one of pins 36. In this manner, offset 23 is quickly and easily demountable from elevator'28. In the conventional type of fork lift truck, the elevator member 28 is provided in the formdescribed and the forks 3| are mounted directly upon the elevator by means of pins 35. I find it convenient to use these same pins as a means for attaching the offset to the elevator; but it is within the scope of my invention to attach the offset and elevator to each other in any suitable manner.

Offset 29 is a stationary frame comprising triangularly shaped top and bottom plates 40 and addition to serving as elevating means, the offset 4| respectively which are interconnected by a plurality of vertically extending structural members. The triangular shape of the top and bottom plates results from the fact that it is desirable to cut away the forward corners of the plates in order not to interfere with swinging movement of the load, and also because the forward corners of these plates are not essential to the structural strength of the offset.

Offset 29 is capable of limited pivotal movement about pins 36, but the dead weight of the parts, as well as the load, holds the offset in the position shown with the offset engaging the lower transverse member 2% of the elevator. Offset 29 is thus, for all practical purposes, fixed relative to the elevator and a part thereof. Offset 23, elevator 28 and bracket 33 combined form means for elevating the load engaging means; and for this function can be modified in shape and construction to fit any given lift truck. In

moves the load forward of the conventional position so that the forks can overhang a stack of lumber or the bed of a truck. The latter is of especial value in loading ordinary trucks as it is necessary to properly balance their loads for transportation to the place of use and to permit safe and easy dumping of the loads. The frontto-rear depth of the offset is about one foot, which permits the fork base to swing from side to side a reasonable amount yet does not shift the load so far forward as to unbalance the loaded lift truck.

Fork base 30 is generally similar in shape to offset 29, comprising a pair of top and bottom plates 42 and 43 respectively which are interconnected by a suitable arrangement of upwardly extending structural members. The spacing be tween plates 42 and 43 is slightly less than the vertical spacing between plates 40 and 4| so that the former plates can fit between the latter ones. as shown in Fig. 3. Fork base 30 and offset 29 are pivotally interconnected by mean-s of a single pivot pin 45. A tubular housing 46 on the fork base provides a bearing in which the pivot pin is journaled. A washer 41 between plates H and 43 provides a thrust bearing for vertical support of the load and the fork base on plate 4|.

Fork base" 30 is designed to have the forward faces of its frame members in a common vertically extending. plane. These members include essentially the uprights between plates 42 and 43 and the downwardly extending flange on plate 42. These members define a single plane which may be'termed a load positioning surface since elements of the load come into contact with them when the forks are fully advanced with respect to the load. If side extensions 49, commonly termed load guards, are employed to increase the effective vertical height of the fork base, then the forward faces of these extensions also lie in this same plane.

The axis of pin 45 is preferably vertical, or substantially so, since it is desirable that the load swing in a horizontal plane. If the axis of the pin is other than vertical, the loadrises or falls a certain amount as it swings from side to side; and this vertical movement of the load is undesirable in combination with the swinging movement.

Sleeve 46 is located as far forwardly as possible on fork base 30 so as to advance to the maximum extent the vertical axis of pin 45 about which the fork base swings with respect to offset 29. Depending upon the con truction used and the thickness of the parts the pin axis ordinarily lies about one or two inches rearwardly of the vertical plane of the forward face of the fork base.

A pair of forks 3| is attached to fork base 30 to project forwardly therefrom. Forks 3| are of conventional construction and are of right angular configuration with one leg extending forwardly in a horizontal direction, and the other leg upwardly therefrom. At the upper end of the latter leg, each fork has a hole through which a bolt 48 passes to hold the fork on the base. Each fork is thus mounted on the fork base to pivot about a horizontal axis; and the weight of the fork and any load carried thereon keeps the back side of the upwardly extending leg of the fork in engagement with the forward edge of bottom plate 43. Plate 43 is shown (Fig. 4) as notched along its forward edge where the forks bear. The notches are deep enough that the forward face of each upwardly extending fork leg is vertical, or substantially so, and in or close to the vertical plane of the forward face of the fork base, as shown by Fig. 3.

In order to swing the load engaging means about its pivotal connection, there is provided driving means which is shown most comprehensively in Fig. 2. The driving means comprises lever arm 50 which is attached, as by welding, at one end to top plate 42 of the fork base. Lever arm 50 is an angular member with upwardly and horizontally extending legs. This design has been selected because of its simplicity and the ease with which it can be adapted to existing trucks; but it will be understood that, like other features of the driving means, I am not limited to any particular design.

The upwardly extending leg of lever arm 50 being attached to the fork base at its center, the horizontal leg of the lever arm passes directly over pivot pin 45. For that reason, the horizontal leg of the arm has an opening 5| to permit insertion and removal of the pivot pin. The rearwardly disposed end of lever arm 50 is attached to traveling block 52 by any suitable type of pivotal connection which is here shown as being of the pin-and-slot type. Pin 53 on traveling block 52 is held in an elongated slot 54 in the end of arm 50 to permit limited relative movement between the pin and the lever arm. A square bushing is placed on pin 53 to increase its bearing against the sides of slot 54. Although it is not necessary, it is preferable to mount on lever arm 55 a bracket 56 which is provided with a similar slot 54 to receive a similar pin 53. Arm 50 is thus formed as a bifurcated member that engages travelling block 52 at two points rather than at a single point.

Block 52 is internally threaded and mounted upon lead screw 53 which is rotatably driven by electric motor 59 through a speed reducer 60. Motor 59 is a low voltage, direct current, reversible motor in order that lead screw 58 may be rotated in either direction; but it is likewise within the scope of my invention to provide two non-reversible m tors arranged so that each motor drives the lead screw in a different direction. It is obvious that this may be done by placing a motor at each end of screw 58, each motor driving through its own speed reducer. Alternatively, a single worm-type speed reducer may be used with a double-ended input shaft at each end of which a motor is connected. The single output shaft is then connected as shown to the lead screw. A worm-and-pinion type of speed reduceris preferred since it is virtually impos- '8 sible to drive it from the output end, and there is then no need for a brake on the motor or lead screw to hold against surges or sudden loads on the travelling block imposed by turning a corner with the lift truck, hitting the load against a stack, or the like.

It will be more apparent from subsequent description that a speed reducer of the irreversible type is desired as it automatically holds the load engaging means in any given position. With this construction, any load applied to the travelling block by arm 50 is unable to cause the lead screw to rotate and the load engaging means stops without overtravel and is locked in any position which it occupies when the electric m0 tor is de-energized.

The electric motor and the lead screw are mounted on top plate 40 of the offset, the lead screw being journaled in suitable bosses 6| that provide radial and thrust bearings for the lead screw. The rotational axis of lead screw 58 is transverse to the fore-and-aft axis 62 of the lift truck so that as the screw rotates travelling block 52 is moved laterally of offset .29 and elevator 28. The corresponding movement of the rearward end of lever 50 swings the load engaging means around the vertical axis of pivot 45, as may be seen best in Fig. 2. When travelling block 52 moves downwardly as viewed in the drawing or toward the left of the operator as he sits facing forwardly in the truck, fork base 30 and the forks thereon are rotated in a clockwise direction, as viewed in Fig. 2. The load engaging means is shown facing straight forward in full lines in Fig. 2, and is shown in dot-dash lines in the extreme position after clockwise rotation. It is possible to produce an equal amount of pivotal movement in a counterclockwise direction from the full line position shown.

The operation of my improved type of load handling mechanism is extremely simple. By means of suitable controls, not shown in the drawings, the truck operator is able to energize selectively the electric motor of the driving means so that lead screw 58 is driven in one direction or the other as desired. This causes movement of the travelling block laterally of the load elevating means which causes rotation of the load engaging means, through the agency of arm 50, in a clockwise or a counterclockwise direction from the normal center position as shown in full lines in Fig. 2.

When the truck operator has a load L of lumber stacked on the forks, as shown in Figs. 3 and 5,'it may be elevated by the load handling mechanism as indicated by the dotted line position in Fig. 1, to bring it over a stack of lumber S. Assume that the truck has advanced to bring the load L directly over the stack S but that the fore-and-aft axis 62 of the truck is not at right angles to the lengthwise dimension of the boards in the stack S. The angle between the actual position of the load and its proper position is equal to the angle 63. The operator then merely energizes driving motor 59 to cause the load engaging means and the load L to rotate in a clockwise direction around pivot 45 through an angle equal to angle 63. At the end of the swinging movement through this angle, the load L is vertically aligned with the stack S, that is the vertical face of the load nearest the operator is brought into parallelism with, or into the place of, the corresponding vertical face of the stack beneath it. In operation, the

truckoperator uses the vertical faces of the stack and of the load which are near or facing him as the elements which he aligns in order to achieve the desired vertical alignment, so that as a practical operation the operators problem is to bring the near face of the load as closely as possible into the plane of the corresponding face of the stack.

When swinging the load, the movement is slow but steady with the type of driving means described above. It has the obvious advantage that as the face of the load reaches the desired position, the operator releases the control switch and the load stops at that position. It does not coast or overtravel as a result of its own momentum but stops in place almost instantly. 7

Proper centering of the load on the stack with respect to placement in a direction endwise of the individual boards of the load, is not so critical and is ordinarily accomplished with suflicient accuracy by centering the truck on the stack S. If the load is centered lengthwise on the forks, then the operator merely approaches the center of the stack in such a manner that the axis 62 of the truck is centered between the ends of the stack. This the operator is ordinarily trained to do; and in turning and maneuvering the truck his objective is at all times to so center the truck with respect to the stack. It is helpful if there is a minimum lateral shift of the load endwise of the stack when the load is rotated in a horizontal plane. It is for that reason that I move the vertical axis of pivot 45 as far forwardly as possible toward the load so that it is substantially at the plane of the front vertical surface of the fork base which is utilized as a load positioning surface when the forks are advanced against the load. As a result, the vertical axis of pivot d substantially coincides with the plane of the rear vertical side face of load L when it is properly positioned on the load engaging means.

Under ideal conditions, if the axis of swinging movement of the load actually coincided with the plane of the rear face of the load, the load would have a minimum movement laterally or endwise of stack S as it rotates through angle 63; and by positioning the axis substantially at this ideal location, the movement of the load L endwise with respect to stack S is minimized and held within allowable limits. For this reason it is always desirable that the operator move the forks as far forward as possible under his load when he picks it up, which is common lift truck practice, for it gives greater stability and capacity to the truck.

It is not ordinarily necessary, or even desirable, that the load be rotatable through a large angle. It is obvious that if a heavy load is rotated too far from the normal position in which it is centered on axis 62, that the truck becomes unbalanced and could be tipped over. It is ordinarily quite ample to obtain all of the advantages of my invention to design the load engaging means to move approximately 10 to 12 either side of the aXis 62. This amount of movement does not shift the center of gravity of the load far enough to cause any danger or difiiculty in handling the truck, yet at the same time it greatly increases the sector or range of movement within which a lift truck can approach a stack and deposit its load thereon without the necessity of any additional turning or maneuvering. As long as the lift truck approaches the stack with its own axis not more than 10 or 12 from a perpendicular to merly and this has the desirable result of giving the truck a shorter turning radius For example,

a truck turning from a narrow alley through a right angle to approach and pick up a load resting on bearing blocks must substantially complete its turn before the forks can slide under the load because the forks must follow a substantially straight path after the tips start underneath the load. In the final part of its travel, the truck must not be moving in an are, or the forks may hit and knock out of position the bearing blocks. A lift truck equipped with the present invention can be moving through an are at the end of its turn with the forks underneath the load but by swinging the forks in the proper direction the fork can be made to follow a substantially straight path with respect to the load to be picked up.

The same is true when a truck is backing away from a load that it has just deposited. Inorder to avoid engaging and possibly knocking out the bearing blocks as the truck withdraws the forks from under the load, it must follow an initially straight path. This path of the forks can be made substantially straight by swinging the forks properly, even though the truck'itself is moving through a curved path. This character istic gives the equivalent of a shorter turning radius and permits the truck to work elfectively in narrower spaces than is possible with the conventional construction.

There is shown in Fig. 6 a modified form of my invention which is the same as the previously described embodiment in all respects except that the power means for swinging the forks and load comprises a hydraulic system for delivering the power in place of the electric motor and lead screw shown in Figs. 2. vIn this modified form,

a stationary piston rod is mounted'on top plate 40 of offset 29, the piston rod being held at its ends in bosses 6|. The piston rod thus extends transversely of the elevating means in the same manner as lead screw 58. Attached at the center of the piston rod is a cylindrical member 61 which subdivides the interior of cylinder 66 into two chambers. Cylinder 66 is slidably mounted on piston rod 65; and suitable packing of any conventional style is provided at the two ends of the cylinder and also on the central wall 61 in order to prevent leakage of the hydraulic Piston rod 65 is hollow at each end, there being a separate fluid passage at each end formed within the'rod and opening to the exterior of the rod at a point adjacent the central cylindrical Wall so that fluid can leave the fluid passage and enter into a selected one of the two chambers inside cylinder 66. To each end of piston rod 65 is attached a hose 68 by means of which fluid under pressure is delivered to the piston rod and thence to the interior of cylinder 66. Hoses 68 are connected to a suitable type of fluid pump, not shown in the drawings, which supplies the fluid under pressure. Such a fiuid'pump isnormally standard equipment on lift trucks since hoist 20 is ordinarily operated by hydraulic pressure.

The travelling block has been modified to assume the shape of collar 52a attached to cylinder 66 to move therewith; The collar is pivotally connected to arm 50 by means of the pin-andslot connection previously described.

In operation, the truck operator introduces fluid such as oil or other suitable liquid through one of lines 68 into the desired chamber within cylinder 66. Since the piston rod 65 is stationary and holds fixed in place the member 61 subdividing the interior of cylinder 66, introduction of fluid under pressure to one of these internal chambers causes that chamber to enlarge and moves the cylinder along piston rod 65. Thus to rotate the load clockwise about pivot 45 to'the full line position shown in Fig. 6, fluid is introduced through the lower hose 68 into the lower one of the two chambers within cylinder 66 which action causes cylinder'66 to move toward the left as viewed by the operator sitting in the seat of the lift truck; Rotation of the load and the load engaging means in the opposite direction is accomplished by introducing fluid through the upper hose 68 into the other chamber within cylinder 66 and simultaneously exhausting fluid from the first chamber. It will be obvious from this description'that the load engaging means may be held in any rotative position by retaining liquid in the two chambers within the cylinder so that the cylinder cannot move with respect to the fixed piston rod. The operation and advantages of a lift truck equipped with hydraulic power means for swinging the load are otherwise the same'as already described above.

From the foregoing disclosure it will be apparent that various changes in the arrangement and construction'of various parts may be made without departing from the spirit and scope of my invention; and consequently I wish it understood that the foregoing is considered as being illustrative of, rather than restrictive upon, the appended claims.

I claim:

1. In an industrial lift truck of the character described having afram'e, an upwardly extending track attached to one end of the'framaand'a power source-carried on the frame, th combination comprising: elevatingmeans movable along the upwardly extending track; load engaging means .pivotallyconnected to the elevating means to swing. in a horizontal plane about a substantially vertical axis substantially coincident with one'edge of a load carried by said means; and driving means controlled by the lift truck operator to swing the load engaging means and the load thereonin a-horizontalplane.

-2. In an industrial lifttruckof the character described having a frame, an upwardly extending. track attached to'oneendof the frame, and a power source carried on the frame, the combination comprising: elevating means movable along the upwardly extending track; load engaging means pivotally connected to the elevating means to swing about a substantially vertical axis; and driving means controlled by the lift truck operator to swing 'the load engaging means, said'driving meanscomprising an electric motor, a lead screw'driven by the electric motor, a travelling block in threaded engagement-with the lead screw and movable laterally of the elevating means, and alever arm attached to the load engaging means and pivotally connected to the travelling block.

3. An industrial lift truck as in claim 2 which also includes an irreversible speed reducer transmitting power to the lead screw from the electric motor.

4. In an industrial lift truck of the character described having a frame, an upwardly extending track attached to one end of the frame, and a power source carried on the frame, the combination comprising: elevating means movable alon the upwardly extending track; load engaging means pivotally connected to the elevating means to swing about a substantially vertical axis; and driving means controlled by the lift truck operator to swing the load engaging means, said driving means comprising an hydraulic cylinder movable laterally of the elevating means, hydraulic means for moving the cylinder, a travelling block attached to the cylinder and movable therewith, and a lever arm attached to the load engaging means and pivotally connected to the travelling block.

5. In an industrial lift truck of the character described having a frame, an upwardly extending track attached to one end of the frame, and a power source carried on the frame, the combination comprising: an elevator member movable along the upwardly extending track in a rectilinear path; a pair of horizontally extending pins on the elevator; an offset mounted on the elevator by engagement with said pins and engaging the elevator at a location below said pins to prevent relative pivotal movement; vertically spaced aligned bearing means on the offset to establish a vertical axis forwardly of said pins and substantially at the forward edge of the offset; a fork base pivotally mounted on the offset to swing relative thereto about said vertical axis over a limited arc; a pair of horizontally extending pins on the fork base parallel to and spaced forwardly of the first mentioned pair of pins; and a pair of angular forks mounted one upon each of said pins on the fork base.

6. In an industrial lift truck of the character described having a frame, an upwardly extending track attached to the frame, and a power source carried on the frame, the combination comprising: an elevator member movable along the upwardly extending track; a fork base extending laterally across the truck and spaced forwardly ofthe elevator member; means pivotally mounting the fork base on the elevator to swing in a horizontal plane about a vertical axis located forwardly of the elevator member and substantially at the load-positioning forward face of the fork base; a pair of angular forks attached to the fork base, one'at each side of the axis of rotation and laterally spaced therefrom, each fork having a forwardly extending load carrying portion and a substantially vertical portion disposed generally rearwardly of the forward face of the fork base whereby said vertical axis is substantially coincident with the rear'face of the load on the forks; and drive means for swinging the fork base and'forks about said vertical axis.

7. .Inan industrial lift truck of the character described having a-frame, an upwardly extending track attached to-the frame, and a-power source carried 'on the-frame, the combination comprising: an elevator member movable along the upwardly extending'track; an offset'mounted on the elevator and'including a pair of vertically spaced bearing supports rigidly interconnected by upwardly extending structural members; bearing means on each of-saicl supports positioned forwardly of the-structural members of the offset and defining a. vertical axis; a fork base pivotally mounted on the ofiset at said bearing means to swing in a horizontal plane about said vertical axis; a. pair of forwardly extending forks mounted on the base at spaced positions located one at either side of said vertical axis; and drive means for swinging the fork base and forks relative to the elevator means through a limited horizontal arc.

THOMAS N. MELIN.

REFERENCES CITED The following references are of record in the file of this patent:

Nmnber 14 UNITED STATES PATENTS Name Date Straight June 5, 1923 Asper Mar. 11, 1941 Cochran Feb. 3, 1942 Westervelt Oct. 29, 1946 Smith Feb. 1, 1949 Boulton May 24, 1949 Lehmann Sept. 12, 1950

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