Sewing – Stitch forming – Feeding work material
Patent
1991-07-24
1992-08-18
Schroeder, Werner H.
Sewing
Stitch forming
Feeding work material
112320, 112237, 112235, 100268, D05B 2902, D05B 2704
Patent
active
051389622
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention pertains to a sewing machine with an upper feed system which consists of an upper feed mechanism having an upper feed foot, a presser foot mechanism having a presser foot, as well as a lifting drive and a pushing drive for the upper feed foot, the feed mechanism having a support which is adjustable in height via a drive connection connected to the housing of the sewing machine, the drive connection including a hydraulic control device.
BACKGROUND OF THE INVENTION
Such a sewing machine is the subject of U.S. Pat. Application No. Ser. 458,701 corresponding to German application P 37,24,786.7-26. It contains a device for automatically adjusting the height position of the upper feed system to the actual working height of the material to be sewn. One possible embodiment of the control device used here is a hydraulic three-position control device. To achieve an idle stroke, this control device has a pre-tensioned spring system arranged between the adjusting piston of the control device and the presser foot as well as the upper feed foot, which spring system produces the range of insensitivity necessary for the three-position control in cooperation with a hydraulic device.
This measure is expensive. The design, which consists of both mechanical and hydraulic components, has a plurality of moving parts which require space and whose hydraulic sealing is expensive.
SUMMARY AND OBJECTS OF THE INVENTION
To improve this device, the basic object of the present invention is to provide a control device whose function is performed predominantly by hydraulic means.
According to the invention, a sewing machine is provided including an upper feed system which consists of an upper feed mechanism having an upper feed foot, a presser foot mechanism having a presser foot, as well as a lifting drive and a pushing drive for the upper feed foot. The upper feed system has a support which is adjustable in height via a drive connection connected to the housing of the sewing machine. The drive connection contains a hydraulic control device with a hydraulic cylinder and an adjusting piston to which the force of reaction arising from the lifting forces acting on the upper feed foot and acting on the presser foot during the sewing process is imparted via a linkage connection. The adjusting piston subdivides the hydraulic cylinder into two chambers. The two chambers are connected to one another via pressure relief means including a first pressure relief valve acting in one direction and a second pressure relief valve acting in another direction (antiparallel-connected pressure relief valves).
The components needed to produce the range of insensitivity are now of a hydraulic nature, as a result of which a simplified, compact design is obtained, and the problems related to sealing are substantially reduced.
The solution according to the invention wherein each pressure relief valve comprises a spring-tensioned check valve and a pressure limiting device arranged downstream of the check valve, leads to an embodiment of simple design of the control device. The measure according to the invention wherein the pressure relief valve contains a sleeve fastened in a hole of the housing of the hydraulic cylinder and each end of this sleeve is connected by an oil passage opening to one of the chambers and a spring-tensioned piston, which is supported by a ball covering and oil passage opening, is displaceably mounted in the sleeve and the piston is arranged in the transition zone to a cross hole in the sleeve, whose diameter is larger than the length of the piston, reduces the mechanism necessary for producing the idle stroke of the control device to a few parts.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter
REFERENCES:
patent: 4187795 (1980-02-01), Norton
patent: 4462320 (1984-07-01), Scholl
patent: 4686917 (1987-08-01), Braun
patent: 4726309 (1988-02-01), Popp
patent: 4936235 (1990-06-01), Klundt
patent: 4981094 (1991-01-01), Stapel et al.
G. M. Pfaff Aktiengesellschaft
Lewis Paul C.
Schroeder Werner H.
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