Conveyors: power-driven – Conveyor section – Reciprocating conveying surface
Reexamination Certificate
1999-05-26
2001-03-20
Bidwell, James R. (Department: 3651)
Conveyors: power-driven
Conveyor section
Reciprocating conveying surface
Reexamination Certificate
active
06202832
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to a vibratory feeder or conveyor that employs leaf springs. Particularly, the invention relates to an improved leaf spring connection for a vibratory feeder or conveyor, the feeder or conveyor having a base member and relatively reciprocating trough connected to the base member by the leaf springs.
BACKGROUND OF THE INVENTION
Vibratory feeders and conveyors are known which employ bar shaped leaf springs connecting a trough to a base member. The leaf springs in these feeders or conveyors may be mounted individually, or in banks of multiple leaf springs to meet the spring rate required by the design of the vibratory equipment. The leaf springs are known to be arranged such that one end of the bank of leaf springs is clamped to the conveying member, for example, the trough of the vibratory feeder, and the other end is clamped to the base member, or to the stationary member in the case of a single mass feeder design. In some designs, a center region of the bank of springs is clamped to structure of the conveying member of the feeder or conveyor, while the ends of the bank of leaf springs are clamped to structure of the base member, forming two spring bank sections.
A problem associated with these prior art designs is that as the spring bank is deflected, the leaf springs are required to elongate due to the geometry of the spring bank configuration. This elongation subjects the leaf springs to very high tensile stress as the leaf springs try to stretch. Also, as the feeder operates in each vibration cycle, the leaf springs are required to first deflect, in a characteristic “S” shaped form, in one direction, then to return to pass through a neutral position, and then to deflect in the opposite direction, and then to return to the neutral position once again to complete the cycle. Thus, with each cycle, the leaf springs experience a fully reversing stress which is detrimental to the useful life of the leaf springs.
The generated forces acting along a spring axis are directed to urge the leaf springs in the spring bank to slip in their clamped connection during some stage of deflection. If the clamping force at the clamped connection is increased to prevent such slippage at this stage of deflection, the resulting tensile stress, combined with the increased bending stress of the spring, particularly at the stress riser location formed where the spring is clamped, is often sufficient to cause a premature failure of a leaf spring as it is deflected back and forth.
There have been some prior art attempts to alleviate the design problem discussed in the previous paragraph, by fixing one end of the leaf springs, say to the base member of the conveyor or feeder, and allowing the other end of the spring to rotate. U.S. Pat. No. 3,845,857 discloses an arrangement of a single mass vibratory feeder wherein one end of a spring bank is connected to a rod mounted in an elastomer bushing such that as the spring element are deflected, the bushing yields, allowing the spring ends to move to provide a substantially simple deflection of the spring. This connection avoids the “S” shape form characteristic of deflecting a leaf spring that is fixed at both ends. While this spring mounting means may reduce the spring stresses involved in the deflection, the resultant spring rate would be reduced to an extent that would make the system impractical for large feeders.
SUMMARY OF THE INVENTION
The present invention contemplates a vibratory conveying apparatus, such as a conveyor or feeder, having a vibratory drive assembly and a trough. The trough is connected to a base member of the vibratory drive assembly via a leaf spring assembly. The leaf spring assembly has an improved spring connection configuration located between the trough and the base member to decrease stress on a leaf spring or springs of the leaf spring assembly to increase the useful life of the leaf spring assembly, while still providing an effective spring rate.
The apparatus includes a vibratory drive arranged between the base member and the trough. The vibratory drive can be an electromagnetic driver, a rotating eccentric weight driver, a rotating crank arm driver, or other type of drive which acts directly on the trough, or acts to indirectly induce vibration through the spring assembly, such as in a base excited conveyor.
The leaf spring assembly preferably includes a plurality of leaf springs stacked together in a spring bank, although a leaf spring assembly having a single leaf spring is also encompassed by the invention. Where a plurality of leaf springs are employed, the springs can be separated by spacers.
In a preferred embodiment, the leaf springs are arranged in a bank and extend substantially perpendicularly to a first direction of vibratory movement of the trough. The leaf springs are connected at a first region to a flexure member and at a second region to structure of the trough. The flexure member is elongated in the first direction, having a base end fastened to the base member and a distal end connected to the leaf springs. The flexure member can flex laterally at its distal end in response to flexing force from the leaf springs.
Preferably, the first region is one end of the leaf springs and the second region is a center region of double length leaf springs. The leaf springs can also include a third region at an opposite end of the double length leaf springs. A second flexure member is connected at its base end to the base member and at its distal end to the third region. The first and second flexure members are configured and arranged in mirror image fashion on opposite lateral sides of the base member.
Each flexure member includes a substantially plate shaped bar member extending substantially along its length from the base end to the distal end. The flexure member includes a clamp element or clamp block connected to the distal end of the bar member. The bar member and the clamp element include openings in registry for accepting one or more leaf spring elements. A fastener proceeds into the distal end of the clamp element to be advanced along the first direction to abut the leaf spring(s) and press the leaf spring(s) against an end surface of the opening to clamp the spring(s) into the clamp element.
The spring attachment mechanism of the present invention is an improvement over the prior known arrangement in that it lowers the spring stresses while maintaining high spring rates for practical designs of large two mass vibratory feeders and conveyors. According to the preferred embodiments of the invention, the characteristic “S” shape form of the deflected leaf spring is retained.
The invention provides an improved means to mount and connect leaf springs used in vibratory feeders and conveyors such that combined tension and bending stresses are minimized. These lower stresses prevent premature spring failure which allows higher vibration strokes than feeders and conveyors using conventional spring clamping methods. The attachment mechanism accommodates a high system spring rate to keep the number and the size of the springs within practical limits.
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Bidwell James R.
FMC Corporation
Rockey Milnamow & Katz Ltd.
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