Rotator for lift truck attachments

Abstract

A device adapted to be attached to the carriage of a lift truck for rotating a load handling attachment about an axis perpendicular to the front face of the carriage. The device has an exceptionally short dimension in a direction parallel to the axis of rotation so as to maximize the load-carrying capacity of the truck. Rotation is produced by engagement between an inner gear with a fixed axis of rotation and external teeth and an outer gear of greater diameter having a larger number of internal teeth. The outer gear is selectively driven in a gyratory eccentric path about the inner gear, thereby rotating the inner gear and thus the attachment through a substantial gear reduction.

Description

BACKGROUND OF THE INVENTION

This invention relates to devices for producing rotary motion, and particularly to devices adapted to be mounted on the carriage of a lift truck for rotating a load handling attachment about an axis extending perpendicular to the carriage and longitudinal of the truck.

In the use of lift trucks it is frequently desirable to rotate a clamp or other load handling attachment about an axis perpendicular to the front face of the lift carriage in order to tilt or turn a load held by the attachment. At the same time it is important that the moment which tends to raise the back of the lift truck off the ground as a result of engaging the load be minimized. Accordingly it is desirable that the device for producing rotary motion have a minimal dimension along its axis of rotation so as to minimize the effective lever arm of the load.

In the past, devices for producing rotary motion at the front of a lift truck have utilized primarily a worm and gear arrangement, the gear being on the axis of rotation and the worm being actuated by a hydraulic motor. However such an arrangement does not sufficiently minimize the aforementioned axial dimension and the resultant load moment, and therefore causes an excessive reduction in the load carrying capacity of the truck. In addition, such arrangement features relatively small gear teeth to achieve the required gear reduction. Such teeth have not proven to be particularly durable under the shock loading and cycling conditions typical of lift truck operations.

A peculiar eccentric gyratory gear drive, sometimes referred to as a "nutating gear assembly," has been known in the past and utilized for certain limited purposes as suggested, for example, by Gilman U.S. Pat. No. 1,566,395 which discloses the gear drive in a drilling machine. While the fundamental principle of such eccentric gear drive is known, its special advantages in lift truck applications have not heretofore been recognized.

SUMMARY OF THE INVENTION

The present invention overcomes the aforementioned problem of minimizing the load moment chiefly by utilizing space in the lateral dimension rather than the axial dimension to produce the desired rotation. The rotator device, which is adapted to be mounted on the face of a lift truck carriage, utilizes the aforementioned eccentric gear drive which features an inner gear with external teeth turning on the axis of rotation of the device engaged in a surrounding manner by an outer gear of greater diameter with internal teeth. The outer gear, supported by eccentric pivots at multiple locations, does not rotate but is driven in a gyratory eccentric path about the inner gear by means of hydraulic cylinders or motors. For each complete gyratory cycle of the outer gear, the inner gear rotates through an angular distance representing the number of teeth difference between the outer gear and the inner gear. Since the gears require much lateral but very little axial space, the moment arm defined by the longitudinal distance from the front axle of the lift truck to the center of gravity of the load is minimized. Moreover the eccentric gyratory gear arrangement is characterized by a relatively small number of very large gear teeth, as opposed to a large number of small teeth normally required in previous rotators to obtain the desired gear reduction, and accordingly the durability of the large teeth is very great.

It is therefore a principal objective of the present invention to provide a novel and improved device adapted to be mounted on a lift truck for rotating load handling attachments, such device having a smaller dimension along the axis of rotation than has heretofore been practical with other rotators and having a greater degree of durability.

The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of one embodiment of the lift truck rotation device shown mounted on a lift truck.

FIG. 2 is an enlarged front view of the rotation device taken along line 2--2 of FIG. 1, with certain elements removed for clarity.

FIG. 3 is a side sectional view of the rotation device taken along line 3--3 of FIG. 2.

FIG. 4 is a detail sectional view of the eccentric pivots taken along line 4--4 of FIG. 2.

FIG. 5 is a schematic fluid power diagram of the drive mechanism of one embodiment of the rotation device.

FIG. 6 is a front view of an alterantive embodiment of the rotation device with certain elements removed for clarity.

FIG. 7 is a side view of the embodiment of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the rotation device 10 is attached by top and bottom hooks 12 and 14 to a pair of attachment bars 16 such as those of a standard dimension established by the Industrial Truck Association (hereinafter referred to as "ITA bars") mounted on the carriage 18 of a lift truck 20. Load handling attachments such as clamps and the like can be attached by any suitable means, such as bolts, to the front of the inner gear of the rotation device and be rotated about an axis 24 which is perpendicular to the front face of the lift truck carriage 18. Both the rotation device and the attachment mounted to it may be selectively raised and lowered by the lift truck carriage.

As shown in FIGS. 2 and 3, the rotation device comprises an inner gear 26 having external teeth 28 rotatably mounted on a hub 30 fixed to a frame 40. The center of the hub 30 is on the axis of rotation 24 of the device and has a hole 31 formed therein for permitting the installation of hydraulic couplings which may be necessary to power the load handling assembly. Rotational friction is reduced by a bearing 32 or bushing of any suitable design. The external teeth 28 of the inner gear are engaged by the internal teeth 34 of a surrounding outer gear 36 which is mounted to the frame 40 by four eccentric pivots 42. The pivots 42 permit the center of the outer gear to oscillate about the axis of rotation 24 in a gyratory path which is eccentric to the axis of rotation 24.

A cover plate 44 with a grooved perimeter 46 is attached to the inner gear 26 by a plurality of bolts 48. The outside diameter of the cover plate is great enough that it partially covers the outer gear 36 in a sandwich-like arrangement illustrated in FIG. 3. A top retainer 50 which rides in the grooved perimeter of the cover plate 44 is attached to the top of the frame 40 by a plurality of bolts 52. A bottom retainer 54 also rides in the grooved perimeter of the cover plate and is attached to the bottom of the frame 40 by a plurality of bolts 56. These two retainers serve to prevent forward axial movement of both the inner and outer gears, but are optional if a bearing 32 of the type capable of resisting axial movement such as a ball bearing is used. A pair of ITA bars 22 may be bolted to the front of the cover plate 44 for accepting a load handling attachment, or alternatively the attachment may be bolted directly to sockets such as 57 provided in the cover plate 44.

Each of the four eccentric pivots 42, illustrated in detail in FIG. 4, comprises a shoulder 58 having a concentric journal 60 mounted in frame 40 and an eccentric journal 62 mounted in the outer gear 36. The shoulder rides in a recess 64 of frame 40. Conventional bearings (not shown) are preferably used in conjunction with the journals 60, 62.

The drive mechanism, shown most clearly in FIGS. 2 and 5, features four double-acting hydraulic cylinders 66, 68, 70 and 72. However, as will be readily understood from the following description, as few as two double-acting hydraulic cylinders would be sufficient. Moreover, hydraulic motors rather than cylinders might be used as explained hereafter with respect to the alternative embodiment. Each of the four cylinders 66 through 72 is mounted to the frame 40 by a respective pivot 74. In order to reduce the axial dimension of the rotating device, the frame 40 has four cut-outs 76 which are positioned so that the cylinders can project rearwardly partially into the spaces provided by the cut-outs. Each piston rod 78 of the four cylinders is connected to the outer gear 36 by a respective pivot 80. Cylinders 66 and 70 exert vertical force on the outer gear 36 and cylinders 68 and 72 exert horizontal force.

A vertical force control valve 82 is mounted to the frame 40 adjacent the cylinder 66. The spool 84 of the valve 82 is pivotally connected by a link 86 to the housing of the cylinder 66 so that the valve 82 will be controlled by the position of the cylinder 66 as it pivots about point 74. A horizontal force control valve 88 is similarly mounted to the frame 40 adjacent cylinder 68 with its spool 90 pivotally connected by link 92 to the housing of the cylinder so that the valve 88 is controlled by the pivotal position of cylinder 68. The vertical force control valve 82 directs hydraulic fluid to the cylinders 66 and 70 while the horizontal force control valve 88 directs hydraulic fluid to cylinders 68 and 72.

Referring primarily to FIG. 5, the four cylinders 66 through 72 and the control valves 82 and 88 are all shown in an arbitrary starting position at which point the outer gear 36 is horizontally centered but at the bottom of its vertical movement. When the operator's manual rotator control valve 94 is actuated to the left in FIG. 5 so as to cause rotation in a given direction, the lift truck pump 96 forces hydraulic fluid through line 98. The fluid passes through control valve 88 into a line 94 which conducts fluid to the primary side 100 of the cylinder 68 (referring to the side of the piston having the greatest surface area) and to the secondary side 102 of cylinder 72. This causes counterclockwise gyration of the outer gear 36 and force fluid out of the secondary side of the cylinder 68 and the primary side of the cylinder 72 into a line 104, through the control valve 88, and through line 106 back to the sump 108.

As the outer gear 36 gyrates counterclockwise, the motion mechanically pivots cylinder 66 and moves the spool of control valve 82 toward the right. This permits fluid from the line 98 to enter the secondary side of the cylinder 66 and the primary side of the cylinder 70 while fluid leaves the primary side of the cylinder 66 and the secondary side of cylinder 70 returning to the sump 108. This action causes the piston rods of cylinders 66 and 70 to aid in gyrating the outer gear 36 counterclockwise. The continuing movement of the outer gear pivots the cylinder 68 upwardly, and likewise the spool of the control valve 88 which tends to center and then subsequently reverse the valve 88. Once the outer gear passes the halfway point of its upward vertical movement, valve 88 is reversed causing pressurized hydraulic fluid to enter through line 104 and exit through line 94 to sump, causing cylinders 68 and 72 to continue to aid the counterclockwise gyratory motion of the outer gear 36. Similarly, the continued motion pivots the cylinder 66 and the spool of the control valve 82 to the left, tending to center and subsequently reverse the control valve 82.

This sequential process continues repeatably causing each of the four cylinders to reciprocate, the vertical pair being 90.degree. out of phase with the horizontal pair. The outer gear 36 moves in a circular gyratory path about the inner gear 26 while each of the four pivots 80 connecting the piston rods 78 to the outer gear similarly travels in a circular pivot path 110. The circular paths of the pivots 80 cause cylinder 66 to oscillate left and right and cylinder 68 to oscillate up and down, thereby permitting the valves to detect, through links 86 and 92 the position of the outer gear and to automatically synchronize the flow of fluid to the cylinders in response to such position. The spools of the respective control valves have small fluid paths 120, 121 which permit some flow of fluid between the sides of the cylinders while the valves are in their transient center positions so as to prevent any pressure-locking of the cylinders. The direction of rotation of the outer gear and thus the device may be reversed by manually actuating the operator valve 94 in the opposite direction.

When the manual valve 94 is placed in its center (off) position, the outer gear 36 is locked into position since fluid cannot flow from one cylinder to another in response to the application of an external force, such as an unbalanced load. For example, in FIG. 5, the pistons of the vertical cylinders 66 and 70 alone could conceivably move since fluid could flow from one side of each of the cylinders through the centered valve 82 to the other, but in order for those pistons to move the pistons of the horizontal cylinders 68 and 72 must also move. However they are restrained since valve 88 cannot be centered at the same time as valve 82 because of their phase difference. Even if the outer gear 36 were stopped in a position leaving a fluid path between the vertical cylinders and the horizontal cylinders, such as a position 45.degree. counterclockwise of the position shown in FIG. 5, the outer gear would still be locked in place. In this position the spool of valve 82 would be to the right and the spool of valve 88 would be in its downward position. Fluid tending to flow out of the cylinders 66 and 70 to permit the outer gear 36 to move, for example, in a clockwise direction would have to flow to the sides of the pistons 68 and 72 which would force the outer gear to move in a counterclockwise direction. Thus the cylinders would be acting against one another and no movement would take place at all.

The pair of eccentrically engaged gears 26 and 36 operate according to a known principle whereby each circular cycle of the outer gear causes the inner gear to rotate through an angle corresponding to the number of teeth difference between the outer gear and the inner gear. The shape and spacing of the teeth on both gears are identical, but the outer gear has more teeth as a result of having a greater inside diameter than the outside diameter of the inner gear. For example, the outer gear 36 of FIG. 2 has sixteen internal teeth 34 while the inner gear 26 has fourteen external teeth 28. This means that each time the outer gear makes a complete cycle, the inner gear will rotate 2/14 of 360.degree., or 51.43.degree.. In seven cycles of the outer gear the inner gear will make one complete rotation of 360.degree., giving a gear reduction of seven to one. The same principle would apply if the outer gear were constrained to rotate about a fixed central axis and the inner gear were driven in a gyratory eccentric path with respect to the outer gear. In such a case the load handling attachment would be mounted on the outer gear.

An alternative embodiment of the invention is shown in FIGS. 6 and 7, differing from the embodiment of FIGS. 1-5 only with respect to the mechanism by which the outer gear 36a is driven. The outer gear 36a includes a pair of lateral extension portions 124 and 126 having a pair of auxiliary eccentric pivots 128, 130 interacting with the frame 40 in a manner similar to the eccentrics 42. However the eccentrics 128, 130 are each rotatably driven through their rear journals by a respective hydraulic motor 132, 134 mounted on the rear side of the frame 40. The lateral spacing of the eccentrics 128, 130 is sufficient that the hydraulic motors may extend rearwardly along the outside of the lift truck mast members 136, to which the carriage 18 is mounted, so as not to interfere with the mast or any projections such as hose reels which may be attached to the mast. In this way the motors do not increase the axial dimension of the rotator device and provide a somewhat simpler mechanism. One or two such motors may be provided, each being actuated by a manual control valve such as 94 (FIG. 5) located in the operator's compartment. Coupling of a motor to an eccentric may be direct, as shown, or by a linkage such as a chain drive.

Although exemplary apparatus has been disclosed and discussed it should be understood that the embodiments shown are not set forth as a limitation on the scope of the invention since other mechanical configurations may also embody the concepts and principles of this invention. Accordingly the terms and expressions which have been employed in the foregoing abstract and specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.

Claims

What is claimed is:

1. In a lift truck having a lifting apparatus at its front end for raising and lowering a load vertically and a load handling attachment for engaging said load to be lifted, a device for rotating said load handling attachment about an axis longitudinal of said lift truck, said device comprising:

a. a frame mounted on the lifting apparatus of said lift truck forwardly thereof between said lifting apparatus and said load handling attachment;

b. an inner gear having external teeth and front and rear faces positioned forwardly of said frame between said frame and said load handling attachment and rotatable about said axis;

c. means for mounting said load handling attachment to the front face of said inner gear so as to be supported thereby;

d. means rotatably mounting said inner gear to said frame from the rear side of said gear for permitting the mounting of said load handling attachment to the front face of said inner gear;

e. an outer gear, with internal teeth adapted to engage said external teeth, movably mounted on said frame between said frame and said load handling attachment in surrounding relation to said inner gear, said outer gear having a greater number of teeth than said inner gear;

f. eccentric means for mounting said outer gear to said frame so as to permit said outer gear to oscillate in a gyratory eccentric path about said inner gear; and

g. power means for oscillating said outer gear in said gyratory eccentric path.

2. The device of claim 1 including a plurality of eccentric pivots for attaching said outer gear at multiple locations to said frame.

3. The device of claim 1 wherein said power means comprises motor means mounted to said frame and coupled with said eccentric means for driving said eccentric means and thereby oscillating said outer gear.

4. The device of claim 3 wherein said motor means is mounted laterally outward from the side of said lifting apparatus in a position extending rearwardly from said frame along the side of said lifting apparatus.

5. In a lift truck having a lifting apparatus at its front end for raising and lowering a load vertically and a load handling attachment for engaging the load to be lifted, a device for rotating said load handling attachment about an axis longitudinal of said truck, said device comprising:

a. a frame mounted on the lifting apparatus of said lift truck forwardly thereof between said lifting apparatus and said load handling attachment;

b. an inner gear movably mounted on said frame forwardly thereof between said frame and said load handling attachment and having external teeth and front and rear faces;

c. an outer gear, having internal teeth adapted to engage said external teeth and having front and rear faces, movably mounted on said frame forwardly thereof between said frame and said load handling attachment in surrounding relation to said inner gear, said outer gear having a greater number of teeth than said inner gear;

d. means for mounting said load handling attachment to the front face of a first one of said gears so as to be supported thereby;

e. pivot means for mounting said first one of said gears to said frame so as to permit it to turn about said axis, said pivot means supporting said first gear from the rear side thereof for permitting the mounting of said load handling attachment to the front face of said first gear;

f. eccentric means for mounting the second one of said gears to said frame forwardly of said frame so as to permit it to oscillate in a gyratory eccentric path about said axis; and

g. power means for oscillating said eccentrically mounted second gear in said gyratory eccentric path.

6. The device of claim 5 including a plurality of eccentric pivots for attaching said second gear at multiple locations to said frame.

7. The device of claim 5 wherein said power means comprises motor means mounted to said frame and coupled with said eccentric means for driving said eccentric means and thereby oscillating said second gear.

8. The device of claim 2 including at least three of said eccentric pivots for constraining the movement of said outer gear to a predetermined eccentric path.

9. The device of claim 1 wherein said eccentric means include means mounting said outer gear to said frame from the rear side of said outer gear for preventing interference with the mounting of said load handling attachment to the front face of said inner gear.

10. The device of claim 1 wherein said inner gear includes a tooth portion and a cover plate portion, said tooth portion being mounted between said frame and said cover plate portion and said load handling attachment being mounted to said cover plate portion, said cover plate portion being of sufficient size to overlap said internal teeth of said outer gear.

11. The device of claim 6 including at least three of said eccentric pivots for constraining the movement of said second gear to a predetermined eccentric path.

12. The device of claim 5 wherein said eccentric means includes means mounting said second gear to said frame from the rear side of said second gear for preventing interference with the mounting of said load handling attachment to the front face of said first gear.

13. The device of claim 5 wherein said first gear includes a tooth portion and a cover plate portion, said tooth portion being mounted between said frame and said cover plate portion, and said load handling attachment being mounted to said cover plate portion, said cover plate portion being of sufficient size to overlap said teeth of said second gear.

14. The device of claim 7 wherein said motor means is mounted laterally outward from the side of said lifting apparatus in a position extending rearwardly from said frame along the side of said lifting apparatus.

15. A device adapted for use on a lift truck for rotating a load handling attachment about an axis longitudinal of said lift truck, said device comprising:

a. a frame adapted to be mounted on the lifting apparatus of said lift truck;

b. an inner gear with external teeth rotatably mounted on said frame so as to turn about said axis;

c. means for mounting said load handling attachment to said inner gear;

d. an outer gear, with internal teeth adapted to engage said external teeth, mounted on said frame in surrounding relation to said inner gear, said outer gear having a greater number of teeth than said inner gear;

e. eccentric means for mounting said outer gear to said frame so as to permit said outer gear to oscillate in a gyratory eccentric path about said inner gear;

f. hydraulic cylinder means attached between said outer gear and said frame for oscillating said outer gear in said gyratory eccentric path; and

g. hydraulic valve means coupled to said cylinder means for automatically controlling the flow of pressurized hydraulic fluid to said cylinder means in response to the position of said outer gear.

16. A device adapted for use on a lift truck for rotating a load handling attachment about an axis longitudinal of said lift truck, said device comprising:

a. a frame adapted to be mounted on the lifting apparatus of said lift truck;

b. an inner gear with external teeth rotatably mounted on said frame so as to turn about said axis;

c. means for mounting said load handling attachment to said inner gear;

d. an outer gear, with internal teeth adapted to engage said external teeth, mounted on said frame in surrounding relation to said inner gear, said outer gear having a greater number of teeth than said inner gear;

e. eccentric means for mounting said outer gear to said frame so as to permit said outer gear to oscillate in a gyratory eccentric path about said inner gear; and

f. a plurality of hydraulic cylinders each attached at one end to said outer gear and at the other end to said frame for oscillating said outer gear in said gyratory eccentric path, at least two of said cylinders being attached so as to exert their respective forces on said outer gear at an angle to one another.

17. A device adapted for use on a lift truck for rotating a load handling attachment about an axis longitudinal of said lift truck, said device comprising:

a. a frame adapted to be mounted on the lifting apparatus of said lift truck;

b. an inner gear movably mounted on said frame and having external teeth;

c. an outer gear, with internal teeth adapted to engage said external teeth, movably mounted on said frame in surrounding relation to said inner gear, said outer gear having a greater number of teeth than said inner gear;

d. means for mounting a first one of said gears to said frame so as to permit it to turn about said axis;

e. eccentric means for mounting the second one of said gears to said frame so as to permit it to oscillate in a gyratory eccentric path about said axis;

f. hydraulic cylinder means attached between said second gear and said frame for oscillating said second gear in said gyratory eccentric path;

g. hydraulic valve means coupled to said cylinder means for automatically controlling the flow of pressurized hydraulic fluid to said cylinder means in response to the position of said second gear; and

h. means for mounting said load handling attachment to said first gear.

18. The device of claim 16 including hydraulic valve means coupled to said cylinders for automatically sequentially controlling the flow of pressurized hydraulic fluid to said cylinders in response to the position of said outer gear, said valve means including means for detecting the position of said outer gear.