WO1982000631A1

WO1982000631A1 - Apparatus for lifting two members relative to a frame

Info

Publication number: WO1982000631A1
Application number: PCT/US1980/001074
Authority: WO
Inventors: L York
Original assignee: L York
Priority date: 1980-08-20
Filing date: 1980-08-20
Publication date: 1982-03-04

Abstract

Conventional lifting mechanisms for positioning materials with respect to a frame such as lift trucks, cranes, and front end loaders frequently have undesirable components of motion. For example, on a conventional fork lift truck that utilizes a parallelogram linkage to elevate the mast and the forks, the tips of the forks trace a vertical path that contains substantial horizontal displacement. This horizontal displacement requires extra maneuvering steps by the operator to avoid having the forks strike nearby objects. The apparatus (45) of the present invention substantially reduces undesirable components of motion by, for example utilizing shortened lifting arms (66, 68) in the parallelogram linkage (64). This reduces the horizontal displacement of the forks (89). The reduction in speed of the mast (74) due to the shortened arms (66, 68) is compensated for by attaching the chain (94) to the linkage (64). In addition, the speed of the forks (89) can be varied by positioning the chain (94) at various attachment points (100) along the length of the parallelogram linkage (64).

Description

Apparatus for Lifting Two Members Relative to a Frame

Technical Field The present invention relates to lifting mechanisms and, more particularly, to apparatus for positioning materials using parallelogram linkages. Such apparatus include conveying systems and material positioning vehicles.

Background Art

Conveying systems and material positioning vehicles often utilize parallelogram linkages to position loads. For example, lift trucks, cranes and front end loaders have such mechanisms. More specifically, a forklift truck having a mast assembly that is supported by a parallelogram linkage is disclosed in U.S. Patent 4,084,715 entitled "Lift Truck with Means to Pivot Mast and the Fork Carriage Thereon" by R. Stedman, issued April 18, 1978. The mast assembly includes two pairs of telescoping uprights and a fork carriage. One set of uprights is elevated with respect to the lift truck using two pairs of parallel lifting arms. The second set of uprights and the fork carriage are elevated by chains that utilize the resulting motion of the parallel lifting arms and the first pair of uprights.

Other patents that describe positioning linkages include U.S. Patent 2,980,271 entitled

OMPI "Lifting Mechanism for Industrial Truck" by ϋlinski issued April 18, 1961; U.S. Patent 3,826,392 entitled "Lifting Device" by Farley issued July 30, 1974 and Danish Patent No. 99672 to Madsen published November 23, 1964.

When parallelogram lifting linkages are used on lift trucks to raise and lower the fork carriage, the tips of the forks describe an arc. In the industry this arcuate path is called swing out and the arc is inherent in parallelogram lifting linkages because the lifting arms are mounted on pins and are thus restricted to travel along circular paths.

The arcuate path of the forks raises three problems. The first problem is that during lifting,. the center of mass of the load is displaced away from the lift truck and a moment arm is created. Such a moment arm can reduce the capacity of the lift truck because either heavier counterweights or smaller loads may be required. Secondly, when lifting a load, the operator must compensate for the forward motion of the mast assembly lifting the load. This forward motion will cause the operator to reposition the vehicle in order to clear any objects adjacent or behind the load being lifted. In addition, the positioning of the forks for engagement with the load to be lifted or lowered is more difficult because as the forks are being moved vertically, the forks are also moving horizontally with respect to the load. This requires further repositioning of the vehicle. Thirdly, the bottom margin of the outer pair of uprights also travels on an arcuate path when the mast assemby is lowered. If the lift truck is abutting an object such as a tote box, the bottom front corner of the outer upright may swing forward during lowering depending on its elevation and may contact the underlying tote box. Moreover, in the lift trucks heretofor described, the speed of the fork carriage is directly related to the speed of the hydraulic cylinder which elevates the mast. The speed is fixed and no flexibility is permitted.

The present invention is directed to overcoming one or more of the problems as set forth above.

Disclosure of the Invention

In one aspect of this invention, an apparatus for lifting two members relative to a frame is disclosed. The apparatus includes a lifting linkage having two arms pivotally connected between the frame and a first member, means for pivotally moving the lifting linkage, a first sheave mounted on the frame,- a second sheave mounted on the first member and an elevating chain attached to the lifting linkage and the second frame and passed around both the first sheave and the second sheave.

The principal purpose of the invention is to reduce the arcuate path or swing out described by the tips of the forks during vertical motion. This purpose is achieved by shortening the length of the lifting arms of the parallelogram linkage.

A further purpose of the present invention is to achieve the same mast lifting height and speed as comparable lift trucks in the industry while using shortened parallel lifting arms. This is achieved by the present invention by utilizing longer uprights and by regulating the speed of the second upright with respect to the first upright.

One feature of the present invention is that the speed of the fork carriage can be varied. This feature is achieved by permitting the mast chain to be attached at various points along the length of the parallelogram lifting arms. Depending on the attachment point, the speed of the second upright is varied with respect to the first upright and in turn, the speed of the carriage and forks is varied.

The present invention also eliminates the problem of interference between the lower end portion of the second upright and an underlying object when the carriage is lowered from an elevated position. This feature is achieved by the use of shorter lifting arms and by positioning the mast within the boundary of the front wheels. The mast is positioned with respect to the truck so that neither upright swings out beyond the leading vertical edge of the front wheels. With the present invention the front wheels of the lift truck can now be used to index the position of the lift- truck against stacks, tote boxes, and the like. Other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure, and the appended claims.

Brief Description of the Drawings

Fig. 1 is a diagrammatic side elevational view, having portions broken away and partially in cross section, of an embodiment of the present invention; and

Fig. 2 is a diagram illustrating the incremental positions and the motion of the mast elevating chain of Fig. 1. Best Mode For Carrying Out The Invention

Referring to the figures, apparatus 78 is shown for lifting two members 80, 82 relative to a frame 50. The apparatus is connected to, for example, a fork lift truck 46 which includes a body 48 having a frame 50. The frame is supported by a pair of front drive wheels 52 and a pair of rear steerable wheels 54. The frame has a mounting tower 56 extending upwardly from the forward end of the lift truck and rearwardly from the center line of the front wheels.

The fork lift truck 46 includes a parallelogram mast lifting linkage 64 connected to the lift truck 46 and the mast 74. The linkage includes two pairs of arms with one pair located on each side of the lift truck. Each pair of arms includes an upper lifting arm 66 and a lower lifting arm 68. The upper and lower arms 66, 68 are each pivotally pinned to a link 72 which is attached to the mounting tower 56 on the frame 50 of the truck. The lower arm 68 is pivotally pinned to link 72 by the pin 102. The other ends of the lifting arms 66, 68 are pivotally pinned to the mast 74 to form a parallelogram. The lower arm 68 is pivotally pinned to the lower upright 80 by the pin 104. The parallelogram linkage is raised and lowered through means for pivotally moving the linkage which is shown as a hydraulic cylinder 76 that is pivotally pinned between the upper lifting arm 66 and the frame 50 of the lift truck and is controllably actuatable as is known in the art. The mast assembly 74 shown includes two pairs of members shown as the uprights^* 80 and 82 which are moveable in response to pivotal movement of the parallelogram linkage 64 between spaced apart elevated positions and relative to one another. The lifting arms 66,68 are pivotally pinned to a first or outer upright 80. Slideably received within the first upright is a second or inner upright 82. As described in detail below, means 78 moves the second upright 82 on rollers 83 relative to the outer upright 80. The mast assembly also includes a carriage assembly 85 which is slideably received within the second upright 82 and is moveable on rollers 87 along the second upright. The carriage 85 incorporates a series of plate members (not shown) to which the lifting forks 89 are mounted. It should be understood that the apparatus can be of other configurations having two members moveable one relative to the other, such as, for example, a single upright structure with a slideable carriage.

The fork carriage elevating apparatus includes a carriage chain 90 connected at one end to an upper end portion of the first upright 80 via a pin 91. The carriage chain is passed over an upper sheave 92 which is attached to an upper end portion of the second upright 82. The other end of the carriage chain is connected to the the carriage 85 via a pin 93- The carriage chain utilizes the relative motion between the first and second uprights 80,82 to elevate the fork carriage 85.

The term sheave, as used herein, includes any guiding device useable to direct a chain as desired; such as sprockets, rotatable or fixed rollers, pins or the like.

The fork carriage elevating apparatus includes a mast chain 9 which is anchored at one end

OMPI to the upper end portion of the second upright 82 via pin 95. The purpose of the mast chain 9 is to elevate the second upright 82 with respect to the first upright 80. The mast chain 94 is passed over a mast sheave 96 which is connected at the upper end portion of the first upright 80. The mast chain 94 is trained under a vehicle mounted sheave 98 and is connected at the other end of the chain 94 to the lower lifting arm 68 by a pin 100. The lower lifting arm 68, Fig. 1, contains a plurality of attachment points for the mast chain 94 so that the position of the pin 100 can be moved between the pivot point 102 and the attachment point 104.

Industrial Applicability Referring to the figures, apparatus 78 is shown for lifting two members 80,82 relative to the frame 50. For example, the lifting forks 89, Fig. 1, are elevated and lowered in response to the motion of the hydraulic actuator 76 acting through the parallelogram linkage 64 and the mast 74. When the hydraulic actuator 7 extends with respect to the frame 50, the parallelogram linkage 64 is elevated. This motion through the arms 66 , 68 raises the first upright 80 and in addition pulls the end of the mast chain 9 at pin 100 upward.

Simultaneously, the second upright 82 moves with respect to the first upright 80 because of two concurrent motions. First, pivotal movement of the lifting arms 64 in an upward direction pulls the mast chain 9 around the sheaves 98, 96 and causes the second upright 82 to elevate. The two sheaves are positioned so that as the pin 100 moves up, the attachment point 95 likewise elevates. This motion occurs irrespective of whether the distance between the mast sheave 96 and the truck sheave 98 is constant or changing. Secondly, upward movement of the lifting arms 64 elevates the first upright 80 and along with it the sheave 96. Mast chain 94 has a fixed length and when the distance between the mast shieve 96 and the truck sheave 98 increases, the distance between sheave 9 and the end of the chain at attachment point 95 must correspondingly decrease.

Concurrently, the fork carriage 85 with the lifting forks 89 is elevated with respect to the second upright 82 by the relative motion between the first upright 80 and the second upright 82. Generation of this relative motion is described immediately above. The upward motion of the second upright 82 relative to the first upright 80 pulls the carriage chain 90 around the upper sheave 92 because the end of the chain is anchored at point 91 which is part of the upper margin of the first upright 80. Thus, the distance between the anchor point 91 and the upper sheave 92 increases and since the chain is inelastic, the distance between the upper sheave 9 and the anchor point 93 on the fork carriage must correspondingly decrease.

In summary, the fork carriage 85 is elevated by four separate motions. First, the linkage 64 raises the entire apparatus. Secondly, pin 100 and in turn the chain 94 attached to it are pulled by the motion of arm 68. This pulls the anchor point 95 and the second upright 82 upward. Thirdly, the distance between sheave 96 and sheave 98 increases and also pulls the anchor point 95 and the second upright 82

OMPI upward. The two last named motions combine to elevate the second upright 82 relative to the first upright 80. Fourthly, the relative motion between the first and second uprights 80,82 increases the distance between anchor point 91 and sheave 92. This causes the carriage chain 90 to reduce the distance between the sheave 92 and the anchor point 93 on the fork carriage 85, thus elevating the carriage.

Lowering the mast 74 and carriage 85 is exactly the reverse of this process and for brevity is not described.

Fig. 2 illustrates how the speed of the mast 74 is incrementall varied. The lower lifting arm 68 contains a plurality of attachment points for the pin 100 connected to the end of the mast chain 94. By anchoring the end of the mast chain 9 at various points along the length of the lower lifting arm 68 the speed of the second upright 82 and in turn the forks 89 can be varied. The angular velocity of the lifting arm 68 about the pin 102 is determined by the speed of the hydraulic actuator 76 and is typically constant. When the pin 100 coincides with the pivot point 102, the mast chain 94 does not move with respect ^■ to the lift truck 46 because the pin 102 is stationary. As the pin 100 is moved away from the pivot point 102, the radius r of motion increases and the mast chain moves with an ever increasing speed until it reaches a maximum at the attachment point 104. Mathematically, if the linear velocity of the mast chain 94 equals V,, then V-, is proportional to V₂(*^) where V is the speed of the mast 74 set by the actuator 76. Thus, the speed of the mast, carriage, and forks can be varied to suit different

OMPI applications for a given hydraulic speed.

Swing out of the forks 86 is reduced by utilizing a parallelogram linkage 64 that incorporates shortened lifting arms 66, 68. The shortened arms reduce swing out by reducing the radius of motion of the arms 64 about the link 72. In other words, the distance between pin 102 and pin 104 is reduced and in turn the horizontal displacement of pin 104 relative to the truck 46 is reduced when the arms 64 swing through an arc. The reduction in lifting height of the fork carriage 85 caused by the shortened arms 64 is compensated by increasing the length of the uprights 80,82. The reduction in speed of the fork carriage 85 caused by the shortened arms is compensated by positioning pin 100 on the arm 68 to achieve a comparable speed.

It should be appreciated from Fig. 1 that use of shortened lifting arms 66,68 also permits the mast 74 to be moved closer to the axle of the front wheels 52. This closer location of the mast reduces the movement of the center of mass of the load during lifting and reduces the magnitude of the moment arm of the load.. In addition, this closer positioning of the mast 74 prevents the second upright 82 from projecting beyond the vertical leading edge of the front wheels 52 during its motion. The front wheels 52 can thus be used to index the position of the fork lift truck 46 against boxes, pallets, and curbs without worry of having the mast 74 come down and strike an abutting object.

Thus, in view of the foregoing it can be seen that by utilizing shortened lifting arms in

OMPI parallelogram linkages, swing out can be substantially reduced. In addition, by attaching the mast chain 94 to one of the lifting arms in the linkage and by providing attachment points for the mast chain at various locations along the length of the lifting arm, the speed of the forks can be varied to suit different applications. This also permits compensation for the reduction in speed due to the use of shortened lifting arms. Other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure, and the appended claims.

O PI

Claims

1. Apparatus (45) for lifting two members (80,82) relative to a frame (50), comprising: a) a frame (50); b) first and second members (80,82) moveable one relative to the other; c) a lifting linkage (64) having two arms (66,68) pivotally connected between the frame (50) and the first member (80); d) means (76) for pivotally moving the linkage (64), said moving means (76) being connected between the linkage (64) and the frame (_.50); e) a sheave (98) mounted on the frame (50); f) . a sheave (96) mounted on the first member (80); and g) an elevating chain (94) attached to the lifting linkage (64) and the second member (82) and passed around said frame mounted sheave (98) and said first member mounted sheave (96).

2. An apparatus (45) as in claim 1 including means (100) connected to the lifting linkage (64) for attaching the elevating chain (94) at different preselected locations along one of said arms (66/68) of said lifting linkage (64).

3« In an apparatus (45) having a frame

(50), first and second members (80,82), an elevating chain (94) and a lifting linkage (64), said lifting linkage (64) having-first and second arms (66,68) each controllably pivotally moveable and pivotally con-

OMPI nected to said frame (50) and said first member (80), said first member (80) being controllably moveable relative to said frame (50) in response to pivotally moving said first and second arms (66,68), said elevating chain (94) being connected to said second member (82) and positioned relative to said first member (80), frame (50) and lifting linkage (64) at a location sufficient for moving said second member (82) relative to said first member (80) in response to moving said first member (80) relative to said frame (50), the improvement comprising: means (78) for moving said second member (82) at different preselected speeds relative to a preselected speed of said first member (80).

4. An apparatus (45) as set forth in claim

3 wherein said moving means (78) includes means (68,100) for moving said elevating chain (94) at different preselected speeds relative to said first member (80) .

5. An apparatus (4.5) as set forth in claim

3 wherein said elevating chain (94) is connected to said lifting linkage (64) and said moving means (78) includes mounting means (100) for connecting said elevating chain (94) at different preselected locations on said lifting linkage (64).

6. A fork lift truck (46), comprising: a) a frame (50); b) a mast (74) having first and second pairs of telescoping uprights (80,82); c) a parallelogram mast lifting linkage

(64) having two -pairs of arms (66,68) connected

OMPI between the frame (50) and the first pair of uprights (80); d) a hydraulic actuator (76) connected between the parallelogram linkage (64) and the frame (50); e) a sheave (98) mounted on the fork lift truck (46); f) a sheave (96) mounted on the first pair of uprights (80); and g) an elevating chain (94) attached to the parallelogram lifting linkage (64) and the second pair of uprights (82) and engaging said truck mounted sheave (98) and said sheave (96) mounted on the first pair of uprights (80).