Biasing mechanism for sewing machine presser foot

1. A sewing machine comprising:

a presser foot;

a drive shaft operably connected to said presser foot which imparts periodic upward movement to said presser foot;

a biasing mechanism operably connected to said presser foot which normally biases said presser foot into a downward position, said biasing mechanism comprising a toggle link having a pivot, a resilient element operably connected to said toggle link on one side of said pivot and said presser foot operably connected to said toggle link on the other side of said pivot;

wherein said resilient element is a compression spring;

a presser foot lifting bar, said presser foot operably connected to said presser foot lifting bar; a mounting plate;

said toggle link operably pivoted relative to said mounting plate;

said resilient element operably fixed relative to said mounting plate;

said toggle link operably connected to said presser foot lifting bar;

a support plate, said toggle link pivoted to said support plate and said resilient element fixed to said support plate;

said support plate pivoted to said mounting plate;

whereby pivoting said support plate relative to said mounting plate pivots said toggle link and resilient element out of biasing engagement with said presser foot lifting bar.

2. The sewing machine of claim 1 further comprising:

a motion generating device operably connected between said support plate and said mounting plate for pivoting said support plate, toggle link and resilient element into and out of biasing engagement with said presser foot lifting bar.

3. The sewing machine of claim 2 wherein said motion generating device is a pneumatic cylinder.

4. A sewing machine comprising:

a presser foot;

a drive shaft operably connected to said presser foot which imparts periodic upward movement to said presser foot; and

a biasing mechanism operably connected to said presser foot which normally biases said presser foot into a downward position, said biasing mechanism having a preload force therein when said presser foot is in a lowermost position;

said presser foot being selectively raisable without increasing the preload force of said biasing mechanism;

wherein said biasing mechanism is selectively pivotable into and out of biasing engagement with said presser foot thereby preventing any increase in the biasing mechanism preload force during selective raising of said pressure foot.

5. The sewing machine of claim 4 wherein said biasing mechanism comprises:

a compression spring; and

a toggle link;

said compression spring operably connected to one end of said toggle link, said presser foot operably connected to the other end of said toggle link.

6. The sewing machine of claim 5 further comprising:

a mounting plate;

a support plate pivoted to said mounting plate;

said compression spring fixed to said support plate;

said toggle link pivoted to said support plate.

7. The sewing machine of claim 5 further comprising a presser foot lifting bar, said presser foot connected to one end of said presser foot lifting bar, said toggle link connected to the other end of said presser foot lifting bar.

8. A sewing machine comprising:

a presser foot;

a drive shaft operably connected to said presser foot which imparts periodic upward movement to said presser foot; and

a biasing mechanism operably connected to said presser foot which normally biases said presser foot into a downward position, said biasing mechanism having a preload force therein when said presser foot is in a lowermost position;

said presser foot being selectively raisable without increasing the preload force of said biasing mechanism;

wherein said biasing mechanism is selectively movable into and out of biasing engagement with said presser foot thereby preventing any increase in the biasing mechanism preload force during selective raising of said pressure foot.