Delay return gas spring

Details Delay return gas spring Delay return gas spring

1999-08-05

2001-01-09

Schwartz, Chris (Department: 3613)

Spring devices

Fluid

Expansible-contractible chamber device

C267S130000

Reexamination Certificate

active

06170809

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to gas springs and more particularly to a gas spring having a delayed return stroke.
BACKGROUND OF THE INVENTION
A typical gas spring for die stamping applications is constructed with an actuating rod connected to a piston slidably received in a cylinder having a cavity which is precharged to a predetermined pressure with an inert gas such as nitrogen. When the rod and piston are forced into the cavity the gas therein is compressed and when the force applied to the rod is removed, the compressed gas within the cavity immediately forces the piston and rod toward its fully extended position.
In some die stamping applications, gas springs adjacent a lower die half may be used to dislodge the stamped part from a cavity of a lower die half. A problem develops on the return stroke of the upper die half when typical gas springs are used because they immediately and rapidly return to their fully extended position and thereby quickly dislodge and lift the die stamped part from the lower die half. At least with parts having a somewhat large surface area, the rapid return of the gas springs toward their extended positions can cause the die stamped part to buckle or flex and thereby adversely affect the quality of the stamped part.
To delay or control the return of the piston and rod to their extended positions, some prior gas springs have utilized mechanical or electronic controls on the gas springs. Such controls are undesirable and increase the cost and complexity of the gas springs. Another type of gas spring, such as that disclosed in U.S. Pat. No. 5,823,513 uses hydraulic fluid in one chamber, compressed gas in another chamber and a delay valve to cause a momentary dwell at the bottom of the gas spring stroke. This dwell is provided to prevent damage to the press among other reasons. A critical aspect of any delay cylinder, is its ability to withstand and/or dissipate the heat generated in use.
SUMMARY OF THE INVENTION
A gas spring with a first gas chamber communicated with a second gas chamber through a calibrated orifice to control the rate of return of gas from the first chamber to the second chamber to thereby control the rate at which a piston rod of the cylinder returns to its extended position. Desirably, the rate of return of the piston rod to its extended position can be made slow enough to prevent damage to a die stamped part as the gas spring lifts the part from a lower die half. The gas spring cylinder assembly contains components which are highly thermally conductive to prevent the gas spring from becoming overheated and to permit an increased number of cycles to be completed in a given period of time. Desirably, the gas spring may be completely self contained and utilize only gas to resist the movement of the piston rod to its retracted position, provide a force to move the piston rod to its extended position, and to control the rate of return of the piston rod to its extended position.
Objects, features and advantages of this invention include providing a gas spring which has a controlled rate of return to its extended position, does not use any hydraulic fluid or other liquid, is self contained, uses only compressed gas uses highly thermally conductive components to increase the dissipation of heat where it is created and to conduct it away from the gas spring, may have a relatively short cycle time, may be used with a surge tank, does not require any active electronic or manual control, and is of relatively simple design and economical manufacture and assembly, and has a long, useful life in service.


REFERENCES:
patent: 3918693 (1975-11-01), Zahid
patent: 4813655 (1989-03-01), Hennells
patent: 5172892 (1992-12-01), Wallis
patent: 5314172 (1994-05-01), Wallis
patent: 5549281 (1996-08-01), Hall
patent: 5823513 (1998-10-01), Stenquist

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