BACKGROUND OF THE INVENTION

In the fabrication or assembly of articles or parts, the parts are commonly transferred along a production or assembly line by an endless transfer conveyor to a series of work stations where each part is worked on, for example, by welding thepart and/or attaching another component to the part. For example, in the construction or assembly of a motor vehicle body, a succession of the car bodies are transferred in a step-by-step or continuous manner to a work station where it is necessary toelevate each body from the conveyor so that certain operations may be performed on the body at the elevated position. It is therefore necessary to have apparatus at the work station which can receive the horizontal conveyor and also raise the body to anelevated position for a, predetermined time, after which the body is lowered back onto the conveyor.

One apparatus which has been constructed and used for elevating a part, such as a vehicle body, from a conveyor at a work station is referred to as the DCT Acculift System which is manufactured by DCT Welding and Assembly in Detroit, Mich. Thissystem incorporates two parallel spaced elongated rails or platens which are positioned adjacent opposite edge portions of the conveyor. Each elongated rail or platen is supported for vertical movement by a pair of horizontal tracks which receive linearbearing blocks pivotally connected to a pair of crank arms mounted on opposite end portions of a horizontal shaft extending parallel to the platen. The horizontal tracks are stabilized and maintained in horizontal positions during vertical movement byvertical linear bearings while the crank arms move the tracks and platens up and down between upper and lower predetermined positions. Each crankshaft for each platen is connected to a gear box, and the two gear boxes are connected by a cross driveshaft so that the crankshafts rotate in unison. One of the gear boxes has an input shaft coupled to the output shaft of a third gear box which is driven by an electric motor. Each of the parallel spaced crankshafts is provided with an overtravel armwhich limits rotation of the crankshaft in one direction, and a mechanical counter-balancing system is used in association with the crank arm on each end of each crankshaft for counter-balancing the weight of the crank arm and the corresponding bearingblock and track support arms.

SUMMARY OF THE INVENTION

The present invention is directed to an improved lifter apparatus of simplified and dependable construction and which requires only one gear reducer and eliminates the need for counter-balancing systems. The apparatus of the invention alsoprovides for synchronized and harmonic movement of the lifting rails or platens and eliminates the need for horizontal linear bearings on the mechanism which supports and moves the rails or platens between their upper and lower positions. The lifterapparatus of the invention also has an overtravel arm mounted directly on the shaft of the drive for the apparatus so that components of the lifting mechanism are not over stressed in an overtravel condition.

In accordance with one embodiment of the invention, a lifter apparatus includes two parallel spaced elongated lift rails or platens each of which is guided for vertical movement by a pair of guide assemblies including linear bearing blocksmounted on corresponding vertical guide rails attached to vertical housings. A bell crank is pivotally supported adjacent each vertical guide assembly, and the two bell cranks for each lift platen are pivotally connected to the corresponding bearingblocks by first link members and to each other by a second link member. A third link member pivotally connects each set of bell cranks for each lift platen to a corresponding crank arm mounted on a crankshaft extending horizontally and laterally belowthe lift platens. A drive unit is connected to one end portion of the crankshaft and includes electric drive motor mounted on a gear reducer and also coupled to an electric brake unit. The output shaft of the gear reducer is coupled to the end portionof the crankshaft and also supports an overtravel arm which is adapted to actuate an overtravel switch. The output shaft of the gear reducer is also coupled to a programmable limit switch and feedback device having a cam switch and resolver or encoderto provide precision control of the electric drive motor and brake unit.

Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of lifter apparatus constructed in accordance with the invention and showing the drive unit in an exploded position;

FIG. 2 is a side view of the lifter apparatus shown in FIG. 1 without the drive unit and with the horizontal lifting platens in their lower position; and

FIG. 3 is a side view similar to FIG. 2 and showing the lifting platens in their upper position.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a steel fabricated open center lifter apparatus 10 includes four vertical guide and support members 12 each of which includes a hollow steel column or housing 14 reinforced by gussets 15 and an attached vertical guide rail(not shown) on which is mounted a linear anti-friction bearing block 17 to provide for low friction vertical movement of each block 17. Each housing 14 is secured to a corresponding base plate 19, and a horizontal tubular beam 22 rigidly connects eachpair of spaced support members 12. A pair of upper and lower collapsible bellows 24 are connected to each bearing block 17 and slidably connect with the corresponding housing 14 to provide protection for the vertical guide rod and linear bearings on thehousing 14.

An L-shaped support bracket 27 is mounted on each bearing block 17, A and the brackets 27 for each pair of spaced support members 12 support an elongated horizontal rail or platen 30 each formed in two sections of square steel tubing joined endto end and having a series of tooling support pads 31 mounted on the top surface of the platen. As shown in FIG. 1, the two pairs of guide and support members 12 are spaced horizontally so that a substantial space is provided between the pair orparallel spaced horizontal platens 30 for receiving a conveyor system between the platens. As mentioned above, the conveyor system (not shown) may incorporate an endless belt or endless chains and be provided with fixtures for supporting a continuousseries of large parts, for example, motor vehicle bodies. When a part arrives at the work station defined between the two pair of guide and support members 12, the pair of elongated rails or platens 30, having fixtures (not shown) mounted on the toolingpads 31, are elevated in unison by a predetermined distance for picking up and raising the part to an elevation where the part may be worked on, for example, by robotic welding equipment. After the work on the part is completed, the rails or platens 30are lowered for returning the part back down to the conveyor where the part is received and advanced to the next work station.

The support and vertical movement of the parallel spaced rails or platens 30 between their normal lower retracted positions (FIG. 2) and elevated upper positions (FIG. 3) are provided by two actuating mechanisms 32 each of which includes a set ofbell cranks 36 and 38 for each pair of guide and support members 12 and each support rail or platen 30. Each set of bell cranks 36 and 38 are pivotally supported by pivot pins or shafts 41 (FIG. 2) mounted on fabricated steel brackets 43 secured to thecorresponding connecting beam 22. A generally horizontal elongated link member 45 pivotally connects each set of bell cranks 36 and 38 by pivot pins or shafts 47, and a generally vertical link member 49 (FIG. 3) pivotally connects each of the bellcranks 36 and 38 to the corresponding bearing block 17 by pivot pins or shafts 52.

Each of the bell cranks 36 is also connected by a generally L-shaped link member 55 to a corresponding crank arm 57 by corresponding pivot pins or shafts 58. The crank arms 57 are rigidly secured to opposite end portions of an elongatedcrankshaft 62 which extends horizontally below the horizontal rails or platens 30. The crankshaft 62 is supported for rotation by a pair of aligned bearing blocks 64 mounted on fabricated steel bearing support members 67 attached to correspondingrectangular base plates 68 extending under and secured to the connecting beams 22. The crankshaft 62 has a projecting end portion 72 (FIG. 1) connected by a coupling 74 to a drive unit 75 effective to rotate the crankshaft 62 in opposite directions andoscillate the crank arms 57 through an angle of about 180.degree. (FIGS. 1 & 2).

The drive unit 75 includes a gear reducer 78 having an input shaft driven by the shaft of a reversible electric motor 80 coupled to the gear reducer 78 and on which is mounted an electrically actuated brake unit 82. Preferably the brake unit 82is an oil shear brake constructed as disclosed in U.S. Pat. No. 4,938,321 which issued to the assignee of the present invention and the disclosure of which is incorporated herein by reference. As disclosed in the patent, the brake unit 82 has springset discs and plates so that the brake is normally applied to the motor shaft when the brake unit is not energized.

The gear reducer 78 has an output shaft 84 which extends through the gear reducer and has one end portion connected by the coupling 74 to the end portion 72 of the crankshaft 62. The gear reducer 78 is mounted on and supported by a fabricatedsteel base 86, and an overtravel arm 88 is rigidly secured to the opposite end portion of the output shaft 84 for rotation with the shaft and the crankshaft 62. An overtravel bumper and switch 90 is engaged by the overtravel arm 88 and is connected tode-energize the motor 80 in the event the control of the electric motor 80 and brake unit 82 do not stop the motor shaft precisely at the desired rotation of the crankshaft 62. A rubber bumper (not shown) is also mounted on the base 86 to form apositive stop for the overtravel arm 88 in the lower position of the support rails or platens 30 (FIG. 2). The output shaft of the gear reducer 78 is also connected to drive a programmable limit switch and feedback device 95 constructed in accordancewith the disclosure of pending U.S. patent application Ser. No. 09/104,023, filed Jun. 24, 1998, the disclosure of which is incorporated by reference.

When the crankshaft 62 is in the position shown in FIG. 2, the pair of elongated rails or platens 30 are in their lower position (FIG. 2) so that the part may be transferred to the lifter apparatus 10 and above the platens and its attachedfixtures by the endless conveyor extending between the platens 30. When the part arrives at the work station having the lifter apparatus 10, the reversible electric drive motor 80 is energized so that the gear reducer 78 rotates the crankshaft 62 in acounter-clockwise direction through approximately 180.degree. to the position shown in FIG. 3 where the platens 30 are elevated to their upper position for raising the part to an elevated position where the part is worked on in some manner. After thework on the part is completed, the motor 80 is energized for rotation of the motor shaft in the opposite direction for rotating the crankshaft 62 clockwise back to the position shown in FIG. 2 so that the part is lowered and transferred back to theconveyor for advancement to the next work station.

From the drawings and the above description, it is apparent that lifter apparatus constructed in accordance with the present invention provides desirable features and advantages. For example, the rotation of the crank arms 57 with the crankshaft62 through an angle of about 180.degree. produces simultaneous rotation of the pair of bell cranks 36 and the pair of bell cranks 38 for generating harmonic vertical movement of the support rails or platens 30 guided by the bearing blocks 17. The slowor soft start and stop of the platens 30 and the supporting part during the vertical movement, results in positioning the platens and the part with high accuracy at the upper and lower positions. This results in higher quality operations being performedon the part at the work station. The crank mechanism of the apparatus 10 is also simple in construction and durable in operation to provide the apparatus with an extended service life, and no counter-balancing system is required. The crank mechanism 32also requires only one gear reducer 78, and the overtravel arm 88 is mounted on the gear reducer shaft so that no overloading stresses are produced in the crank mechanism 32. Since both of the crank arms 57 are mounted on a common crankshaft 62, the upand down movement of the platens 30 is precisely synchronized,

While the form of lifter apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein withoutdeparting from the scope and spirit of the invention as defined in the appended claims.

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