Hemming machine

Details Hemming machine Hemming machine

1999-11-01

2001-02-06

Jones, David (Department: 3725)

Metal deforming

With means to drive tool

Including screw-actuated tool support

C072S448000, C072S323000, C072S381000, C072S384000, C029S243580, C100S099000, C083S631000

Reexamination Certificate

active

06182492

ABSTRACT:

BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to hemming machines and, more particularly, to a sheet metal hemming machine utilizing a vertically movable nest supporting the sheet metal part to be hemmed to press against stationary dies which are moved into and out of an operating position.
II. Description of the Prior Art
Typically sheet metal hemming devices utilize hydraulic cylinders for imparting vertical movement to the impacting punch or nest. The vertical movement provided by the cylinders is often erratic which slows down the operation of the hemming process and otherwise causes inaccuracies. This is particularly critical where multiple actuating hydraulic cylinders are employed, even if in final, this compliance allows a perfect balancing of the hemming effort on each edge of the part.
A major disadvantage of the previously known use of hydraulic cylinders for hemming machines is the inevitable leakage of the hydraulic fluid and the resulting mess created by such leakage.
There have, however, been previously known hemming machines which utilize electric servo-motors in order to vertically displace the nest to perform the hemming operation. These previously known electric motor actuated hemming machines, however, have required a complete synchronization between the rotation of the actuating shafts in order to achieve the vertical displacement of the nest. In practice, however, such absolute synchronization between the rotatable shafts cannot be achieved in every situation, and does not allow a perfect balancing of the hemming effort applied on each edge of the part, in both pre-hemming and hemming positions. Furthermore, any lack of synchronization between the electric motor actuated shafts may result in seizure and even destruction of the hemming machine.
SUMMARY OF THE PRESENT INVENTION
The present invention provides a hemming machine which utilizes electric servo-motor actuated shafts for vertically displacing the nest which overcomes all of the above-mentioned disadvantages of the previously known devices.
In brief, the hemming machine of the present invention includes a base and a nest for supporting a sheet metal part to be hemmed. At least one die is mounted to the base and is movable between an extended position in which the die registers with the nest, and a retracted position in which the die is retracted from the nest thus permitting the completed hemmed part to be removed from the nest as well as a new sheet metal part to be placed on and supported by the nest.
At least three and preferably four elongated and externally threaded shafts each have their lower ends rotatably mounted to the base so that the shafts are spaced apart and parallel to each other. An electric servo-motor is operatively coupled with each shaft so that, upon actuation of the master servomotor, the other slave servo-motors drive the shaft substantially, although as a practical matter not entirely, in synchronism with the master servo-motor.
Means are mounted to the nest for threadably receiving the second or upper end of each shaft and this threadable receiving means is fixed against rotation to the nest. Consequently, rotation of the threaded shafts vertically displace the nest due to their coaction with the threadable receiving means.
In the preferred embodiment of the invention, the threadable receiving means comprises a nut which is threadably engaged with the shaft. A first externally splined annulus is coaxially disposed around the nut and this first annulus is secured against movement to the nest.
A second externally splined annulus is then coaxially disposed around and secured to the nut so that the second annulus is axially spaced from and coaxial with the first annulus. An internally splined tube is then disposed around the first and second annuli so that the internal splines on the tube intermesh with the external splines on the annuli. Consequently, the annuli, together with the internally splined tube, preclude rotation of the nut relative to the nest so that rotation of the shaft axially displaces the nut together with the nest.
In order to permit angular or slight radial displacement of the shafts relative to each other as would occur unless the shafts are absolutely synchronized for rotation to each other, the nut is swivelly mounted to the nest. In the preferred embodiment of the invention, this swivel mounting means comprises a thrust bushing having a semispherical surface and a bushing retainer which secures the bushing against pure vertical movement to the nest. A complementary semispherical surface formed on the nut abuts against the semispherical surface on the bushing to thereby permit limited swiveling movement of the nut relative to the nest. Such limited swivel capability of the nut relative to the nest is sufficient to compensate for limited non-synchronism of the rotation of the threaded shafts, and let the servo-motor controller react against any incidental situation.
In the preferred embodiment of the invention, the bearing retainer is secured to the nest by compression washers, preferably Belleville washers, which will compress whenever the axial force exerted on the compression washer exceeds a predetermined minimum amount. Thus, in the event that a machine jam or other failure results in an excessive axial force exerted between the nut and bearing retainer relative to the nest, the compression washers will compress slightly thus axially displacing the bushing retainer relative to the nest. Any such displacement of the bearing retainer relative to the nest is detected by a sensor which can then be used to terminate the operation of the hemming machine thereby protecting the hemming machine against destructive forces which might otherwise occur (kinetic energy generated by motor inertia).


REFERENCES:
patent: 5454261 (1995-10-01), Campian
patent: 5488880 (1996-02-01), Sartorio
patent: 5669296 (1997-09-01), Newton

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