Top feed systems that include a top feed dog and/or a feed belt for feeding work pieces through a sewing station are known. In such systems, the fabric material will be engaged between the top feed dog and a bottom feed dog, so as to pull the fabric material therebetween for feeding the fabric material through the sewing station. Such top feed systems generally are used for feeding heavier gauged fabric materials by compressing the fabric material against the bottom feed dogs and pulling the material forward in a walking motion as the material is sewn. However, with especially thick, heavy gauge fabric materials such as foamed pads and/or border materials for mattresses, the thickness of such textile materials can create a problem during sewing when the presser foot of the sewing station must apply added pressure to compress the fabric material to an amount sufficient to enable the needle to penetrate far enough so that the stroke of the loopers engages the threads of the sewing needle. Without such compression, the needle will not penetrate fully through the fabric and thus the threads being sewn by the needle accordingly will not be engaged by the loopers, resulting in an improperly sewn work piece that must be discarded or resewn. The problem with applying such added pressure to the presser foot is, however, that the resulting tighter engagement of the presser foot with the material work piece tends to create friction or drag that can hinder the movement of the material and resist the clamping engagement between the top and bottom feed dogs. As a result, as the top feed dog engages and bears against the fabric, instead of moving the fabric under the presser foot, the top feed dog can tend to pick or tear the fabric material as it moves thereover, resulting in an unacceptable work piece.
In an effort to address this problem, prior art devices have included systems that apply pressure to the presser foot, such as through springs or cylinders, during the penetration of the needle and engagement of the loopers therewith. Thereafter, as the needle stroke or cycle is completed and the needle is raised, a mechanical linkage tied to the feed dogs causes the presser foot to be raised as the top feed dog is lowered into engagement with the material in its stepping or walking motion. As the feed dogs complete the pulling cycle and the top feed dog begins to be raised, the mechanical linkage thereafter allows the presser foot to be lowered back down into compressive engagement with the upper surface of the fabric. A problem that exists with such a rigid, structured mechanical linkage is that it tends to significantly limit the speed of operation of the sewing machine, thus limiting the production rates of such sewing systems. In addition, these mechanical linkages are hard to lubricate because they cannot be sealed and thus typically are subject to significant friction and vibration. Further, the lubrication of such systems must be limited to avoid soiling or contaminating the fabrics being sewn with excess oil or other applied lubricants.
Accordingly, it can be seen that a need exists for a system that controls the application of pressure to a presser foot during the sewing of thicker or heavier gauge fabrics that enables greater production rates and speeds and addresses the foregoing related and unrelated problems in the art.