Thread tensioning device

Claim 2

A thread tensioning system for a sewing machine comprising means for tensioning the bobbin thread including: a. a ferromagnetic bobbin, onto which said thread is wound; b. a ferromagnetic bobbin case for housing said bobbin, said bobbin case being rigidly and removably mounted to a support member; c. an electromagnetic to provide a source of magnetic flux; d. radial flux guiding means rigidly connected to an end of said electromagnet for guiding magnetic flux radially between said bobbin and said bobbin case and said electromagnet; e. axial flux guiding means rigidly connected to the other end of said electromagnet for guiding magnetic flux axially between said electromagnet and said bobbin and said bobbin case, wherein said radial flux guiding means, said axial flux guiding means, said bobbin, said bobbin case and said electromagnet form a closed magnetic circuit; means for supplying electrical current to said electromagnet to create said magnetic flux therein proportionately to the magnitude of said electrical current, thereby causing tension on the thread to be created by the combination of the magnetic drag resisting rotation of said bobbin in said magnetic flux and the frictional engagement between said bobbin and said bobbin case caused by said bobbin being urged against an interior wall of said bobbin case by said magnetic flux; and means for varying said electrical current to vary said magnetic flux and thereby vary said thread tension.

Claim 3

The thread tensioning system of claim 1, wherein said radial flux guiding means includes a ferromagnetic bifurcated arm positioned radially with respect to said bobbin case, said arm having two extensions forming a semicircular wall around and in close proximity to said bobbin case.

Claim 4

The thread tensioning system of claim 1, wherein said axial flux guiding means includes: a. an end plate having a lower end rigidly attached to the other end of said electromagnet; b. a ferromagnetic rod having an end rigidly attached to an upper end of said end plate; c. a sleeve for slideably supporting said rod; d. a bracket for rigidly supporting said sleeve; and e. a rail upon which said bracket is rigidly mounted and said end plate is slideably mounted for moving said electromagnet axially away from said bobbin case to provide access to said bobbin.

Claim 5

The thread tensioning system of claim 3 which further includes an air cylinder rigidly attached to said rail, said air cylinder having a plunger connected to said end plate for automatically moving said electromagnet axially away from said bobbin case.

Claim 6

The thread tensioning system of claim 1, wherein said means for supplying electrical current to said electromagnet includes: a. a variable output d.c. power supply; and b. an ammeter connected in series with said power supply and said electromagnet, said ammeter being used to indicate the thread tension being applied by said thread tensioning system at any given time.

Claim 7

The thread tensioning system of claim 5, wherein said means for supplying electrical current is connected to a plurality of electromagnets of similar thread tensioning systems for equalizing the bobbin thread tensions amongst such systems.

Claim 8

The thread tensioning system of claim 1, which further includes electromagnetic means for tensioning an upper needle thread comprising: an electromagnetic assembly having a. a central ferromagnetic sleeve; b. an electromagnetic coil wound around a portion of and rigidly secured to said sleeve; c. a ferromagnetic first bushing end plate radially oriented and rigidly secured to one end of said sleeve proximate an end of said coil; d. a second bushing end plate radially oriented and rigidly secured to an interior portion of said sleeve proximate the other end of said coil; a ferromagnetic casing enclosing said electromagnetic assembly, said casing being slideably mounted upon said sleeve and said first and second bushing plates, with an end portion of said sleeve projecting therefrom; a thread guide means assembly mounted upon said projecting portion of said sleeve including: a. an outer plate rigidly attached to an end of said casing, and slideably mounted on said projecting portion of said sleeve; b. an inner plate adjacent said outer plate; c. a spacer adjacent said inner plate, at least one of said inner plate and said spacer being ferromagnetic; means for supplying electrical current to said electromagnetic assembly to create a magnetic flux passing through a magnetic circuit including said electromagnetic assembly, said sleeve, said casing, and at least one of said spacer and said inner plate, causing said casing to urge said outer plate against said inner plate to tension said needle thread therebetween, the magnitude of said tensioning being proportional to the magnitude of said electrical current; and means to vary said electrical current to said electromagnetic assembly to thereby vary said needle thread tension.

Claim 9

The thread tensioning system of claim 7 wherein said means for tensioning the needle thread includes: a. said sleeve having a central bore; b. a plug mounted in the core of said sleeve near the end of said sleeve proximate said first bushing; c. an adjusting bolt threadably mounted through the other end of said casing proximate said first bushing, said screw bearing against said plug for increasing or decreasing the gap between said casing and said first bushing to vary the magnetic coupling therebetween.

Claim 10

The thread tensioning system of claim 7 wherein said first and second bushing end plates are Teflon coated for minimizing friction between said plates and said case.

Claim 11

The thread tensioning system of claim 7 wherein said means for supplying electrical current to said electromagnet coil of said means for tensioning the needle thread, includes: a. a variable output d.c. power supply; and b. an ammeter connected in series with said power supply and said electromagnet coil, said ammeter being used to indicate the tension being applied by said thread tensioning means upon said needle thread at any given time.

Claim 12

The thread tensioning system of claim 10 wherein said means for supplying electrical current is connected to a plurality of electromagnet coils of thread tensioning systems similar to said needle thread tensioning means to equalize the needle thread tensions amongst such systems.

Claim 15

The thread tensioning apparatus of claim 12 wherein said thread tensioning apparatus further includes: a. said sleeve having a central core; b. a plug mounted in the core of said sleeve near the end of said sleeve proximate said first bushing; c. an adjusting bolt threadably mounted through the other end of said casing proximate said first bushing, said screw bearing against said plug for increasing or decreasing the gap between said casing and said first bushing to vary the magnetic coupling therebetween.

Claim 16

The thread tensioning apparatus of claim 12 wherein said first and second bushing end plates are Teflon coated for minimizing friction between said plates and said case.

Claim 17

The thread tensioning apparatus of claim 12 wherein said means for supplying electrical current to said electromagnet coil further includes: a. a variable output d.c. power supply; and b. an amMeter connected in series with said power supply and said electromagnet coil, said ammeter being used to indicate the tension being applied by said thread tensioning means upon said thread at any given time.

Claim 18

The thread tensioning apparatus of claim 15 wherein said means for supplying electrical current is connected to a plurality of electromagnet coils of thread tensioning apparatus similar to said thread tensioning apparatus to equalize the thread tensions amongst such apparatus.