Lifter apparatus for raising and lowering a part

Information

  • Patent Grant
  • 6422536
  • Patent Number
    6,422,536
  • Date Filed
    Wednesday, July 12, 2000
    24 years ago
  • Date Issued
    Tuesday, July 23, 2002
    22 years ago
Abstract
A pair of horizontally spaced and horizontally extending part support rails or elongated platens are each guided and supported for vertical movement by a pair of guide and support members having linear bearing blocks mounted on vertical guide rails attached to corresponding vertical housings. A bell crank is pivotally supported adjacent each housing and is pivotally connected to the corresponding bearing block by a first link member. Second and third link members pivotally connect each pair of bell cranks for each platen to each other and to a crank arm mounted on a horizontal crankshaft extending laterally below the platens. A combined electric motor and gear reducer have an output shaft coupled to one end portion of the crankshaft, and an electric brake unit is connected to the motor shaft. An overtravel arm is also secured to the output shaft of the gear reducer and actuates an overtravel switch connected to control the electric motor. The output shaft also drives a programmable limit switch and feedback device for precisely controlling the electric motor and brake unit according to the position of the platens.
Description




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 the part 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 to elevate 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 an elevated 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. This system 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 linear bearing 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 by vertical 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 drive shaft 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 arm which 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 bearing block 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 also provides 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 lifter apparatus 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 blocks mounted 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 bearing blocks 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 below the 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 portion of 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 encoder to 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 each pair 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 the housing


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 end to 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 or parallel 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 continuous series 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 tooling pads


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


30


are 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 of bell 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 the corresponding 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 bell cranks


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 elongated crankshaft


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 corresponding rectangular 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 and oscillate the crank arms


57


through an angle of about 180° (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


82


is 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 spring set 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 fabricated steel 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 to de-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 a positive 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 accordance with 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 attached fixtures 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 a counter-clockwise direction through approximately 180° 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 the work 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 the conveyor 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 crankshaft


62


through an angle of about 180° 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 slow or 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 performed on 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


32


also 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 up and 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 without departing from the scope and spirit of the invention as defined in the appended claims.



Claims
  • 1. Apparatus for raising and lowering a part between a lower position and an upper position, said apparatus comprising horizontally spaced platens adapted to receive the part from a conveyor extending between the platens, a set of guide members supporting said platens for generally vertical movement between said lower position and said upper position, each of said guide members including a linear bearing member connected to one of said platens and supported by a generally vertical guide rail, a generally horizontal crankshaft extending below said platens and between said guide members, a set of crank arms mounted on said crankshaft, at least one pivotally supported bell crank member for each of said crank arms, a first link member pivotally connecting each of said crank arms to the corresponding said bell crank member, a second link member pivotally connecting each of said bell crank members to the corresponding said platen, and a power operated reversible drive connected to rotate one end portion of said crankshaft in opposite directions to provide smooth harmonic vertical movement of said platens and the part between said upper and lower positions.
  • 2. Apparatus as defined in claim 1 wherein said platens are elongated and extend generally horizontally in generally parallel spaced relation, a set of horizontally spaced said guide members supporting each of said platens for vertical movement, a corresponding set of said bell crank members for each of said platens, and a third link member pivotally connecting each set of said bell crank members to provide for oscillation of all of said bell crank members in unison.
  • 3. Apparatus as defined in claim 1 wherein said power operated drive comprises a reversible electric drive motor having a motor shaft connected to a gear reducer having an output shaft connected to said end portion of said crankshaft, and a power operated brake unit connected to said electric motor shaft.
  • 4. Apparatus as defined in claim 3 and including a programmable limit switch and feedback controller driven by said output shaft of said gear reducer for controlling the operation of said drive motor.
  • 5. Apparatus as defined in claim 3 and including an overtravel arm mounted on said output shaft of said gear reducer, and an overtravel control switch for said motor and positioned to be actuated by said overtravel arm.
  • 6. Apparatus as defined in claim 3 wherein said brake unit comprises a housing enclosing a stack of oil shear brake discs and plates, and springs normally urging said stack of brake discs and plates together for stopping said motor shaft.
  • 7. Apparatus as defined in claim 1 wherein each of said guide members comprises a generally vertical housing enclosing the corresponding said guide rail, and a flexible bellows supported by each said housing and connected to the corresponding said bearing member.
  • 8. Apparatus for raising and lowering a part between a lower position and an upper position, said apparatus comprising generally parallel spaced and generally horizontal elongated platens adapted to receive the part from a conveyor extending between the platens, a set of guide members supporting each of said platens for generally vertical movement between said lower position and said upper position, a generally horizontal crankshaft extending below said platens and between said sets of guide members, a crank arm mounted on said crankshaft for each said set of guide members, a set of pivotally supported bell crank member for each of said crank arms, a first link member pivotally connecting each of said crank arms to one of said bell crank members of the corresponding said set of bell crank members, a second link member pivotally connecting said bell crank members of each said set, a third link member connecting each of said bell crank members to the corresponding said platen, and a power operated reversible drive connected to rotate one end portion of said crankshaft in opposite directions to provide smooth harmonic vertical movement of said platens and the part between said upper and lower positions.
  • 9. Apparatus as defined in claim 8 wherein said power operated drive comprises a reversible electric drive motor having a motor shaft connected to a gear reducer having an output shaft connected to said end portion of said crankshaft, and a power operated brake unit connected to said electric motor shaft.
  • 10. Apparatus as defined in claim 9 and including an overtravel arm mounted on said output shaft of said gear reducer, and an overtravel bumper and control switch for said motor and positioned to be engaged by said overtravel arm.
  • 11. Apparatus as defined in claim 9 and including a programmable limit switch and feedback controller driven by said output shaft of said gear reducer for controlling the operation of said drive motor.
  • 12. Apparatus as defined in claim 9 wherein said brake unit comprises a housing enclosing a stack of oil shear brake discs and plates, and springs normally urging said stack of brake discs and plates together for stopping said motor shaft.
  • 13. Apparatus as defined in claim 8 wherein each of said guide members comprises a linear bearing member connected to one of said platens and supported by a generally vertical guide rail.
  • 14. Apparatus as defined in claim 13 wherein each of said guide members comprises a generally vertical housing enclosing the corresponding said guide rail, and a flexible bellows supported by each said housing and connected to the corresponding said bearing member.
  • 15. Apparatus for raising and lowering a part between a lower position and an upper position, said apparatus comprising generally parallel spaced and generally horizontal elongated platens adapted to receive the part from a conveyor extending between the platens, a set of generally vertical guide members supporting opposite end portions of each of said platens for generally vertical movement between said lower position and said upper position, a generally horizontal crankshaft extending between said sets of guide members, a crank arm mounted on said crankshaft for each said set of guide members, a set of pivotally supported bell crank members for each of said crank arms, a first link member pivotally connecting each of said crank arms to one of said bell crank members of the corresponding said set of bell crank members, a second link member pivotally connecting said bell crank members of each said set, a third link member connecting each of said bell crank members to the corresponding said platen, a reversible electric motor and gear reducer drive having an output shaft connected to rotate one end portion of said crankshaft in opposite directions to provide smooth harmonic vertical movement of said platens and the part between said upper and lower positions, and an electrically actuated brake unit mounted on said motor and connected to stop a shaft of said motor.
  • 16. Apparatus as defined in claim 15 and including an overtravel arm mounted on said output shaft of said drive, and an overtravel bumper and control switch for said motor and positioned to be engaged by said overtravel arm.
  • 17. Apparatus as defined in claim 15 and including a programmable limit switch and feedback controller driven by said output shaft of said drive for controlling the operation of said motor.
  • 18. Apparatus as defined in claim 15 wherein said brake unit comprises a housing enclosing a stack of oil shear brake discs and plates, and springs normally urging said stack of brake discs and plates together for stopping said motor shaft.
  • 19. Apparatus as defined in claim 15 wherein each of said guide members comprises a linear bearing block connected to one of said platens and supported by a generally vertical guide rail, a generally vertical housing attaching the corresponding said guide rail, and a flexible bellows supported by each said housing and connected to the corresponding said bearing block.
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Number Name Date Kind
4324386 Gagnon et al. Apr 1982 A
4938321 Kelley et al. Jul 1990 A
5050844 Hawk Sep 1991 A
5120022 Kubik Jun 1992 A
5186282 Everhard et al. Feb 1993 A
5199686 Fletcher Apr 1993 A
6059263 Otema et al. May 2000 A