Speed detector for sewing machines

Claim 2

A speed detector for a sewing machine comprising a rotor rotatable with a drive shaft of the sewing machine, a stator fixed to a housing of the sewing machine, said rotor and stator being formed of a ferromagnetic material and each having a multitude of teeth which face in opposition to the teeth of the other forming a gap therebetween, a permanent magnet forming a closed loop magnetic circuit with said rotor and stator, a coil which intersects the magnetic flux of said closed loop magnetic circuit to generate a voltage which is used to generate a train of pulses at a frequency proportional to the rotational speed of said sewing machine through an amplifier and a waveshaping circuit, further comprising an integrating circuit connected to one of said amplifier and waveshaping circuit.

Claim 3

A speed detector for a sewing machine comprising a rotor rotatable with a drive shaft of the sewing machine, a stator fixed to a housing of the sewing machine, said rotor and stator being formed of a ferromagnetic material and each having a multitude of teeth which face in opposition to the teeth of the other forming a gap therebetween, a permanent magnet forming a closed loop magnetic circuit with said rotor and stator, a coil which intersects the magnetic flux of said closed loop magnetic circuit to generate a voltage which is used to generate a train of pulses at a frequency proportional to the rotational speed of said sewing machine through an amplifier and a waveshaping circuit, further comprising a second permanent magnet to form a second closed loop magnetic circuit having a common magnetic path with the first-mentioned magnetic circuit, and a second coil disposed in said second magnetic circuit, the first-mentioned coil and said second coils connected in a series circuit so that the voltages developed respectively in said coils are constructively added.

Claim 4

A speed detector for a sewing machine comprising a rotor rotatable with a drive shaft of the sewing machine, a stator fixed to a housing of the sewing machine, said rotor and stator being formed of a ferromagnetic material and each having a multitude of teeth which face in opposition to the teeth of the other forming a gap therebetween, a permanent magnet forming a closed loop magnetic circuit with said rotor and stator, a coil which intersects the magnetic flux of said closed loop magnetic circuit to generate a voltage which is used to generate a train of pulses at a frequency proportional to the rotational speed of said sewing machine through an amplifier and a waveshaping circuit, further comprising a second permanent magnet to form a second closed loop magnetic circuit having a common magnetic path with the first-mentioned magnetic circuit, and a second coil disposed in said second magnetic circuit, the first-mentioned coil and said second coils connected in a series circuit so that the voltages developed respectively in said coils are constructively added.

Claim 5

A speed detector having a rotary shaft adapted for connection to a rotating body, comprising: a ring-shaped permanent magnet uniformly magnetized in a direction parallel to the axis of said rotary shaft; a ring-shaped, internally toothed ferromagnetic member; an externally toothed ferromagnetic circular member disposed inside of said ring-shaped ferromagnetic member with a spacing therefrom to form an air gap between the teeth of each said ferromagnetic member and the teeth of the other ferromagnetic member, said ferromagnetic members forming a closed loop magnetic circuit with said permanent magnet and disposed rotatably with respect to each other by revolution of said rotary shaft so that said air gap varies periodically at a rate proportional to the speed of revolution of said rotary shaft; a ring-shaped coil disposed in said closed loop magnetic circuit to develop a voltage at a frequency proportional to the rate of variation of said air gap; a second ring-shaped ferromagnetic member disposed in a side-by-side relationship with said ring-shaped permanent magnet opposite to the first-mentioned ring-shaped ferromagnetic member, and a second ferromagnetic circular member rotatable with and axially spaced from the first-mentioned ferromagnetic circular member and disposed inside said second ring-shaped ferromagnetic member to form a second air gap therebetween, wherein said coil is located between said first and second ferromagnetic circular members.

Claim 6

A speed detector having a rotary shaft adapted for connection to a rotating body, comprising: a ring-shaped permanent magnet uniformly magnetized in a direction parallel to the axis of said rotary shaft; a ring-shaped, internally toothed ferromagnetic member; an externally toothed ferromagnetic circular member disposed inside of said ring-shaped ferromagnetic member with a spacing therefrom to form an air gap between the teeth of each said ferromagnetic member and the teeth of the other ferromagnetic member, said ferromagnetic members forming a closed loop magnetic circuit with said permanent magnet and disposed rotatably with respect to each other by revolution of said rotary shaft so that said air gap varies periodically at a rate proportional to the speed of revolution of said rotary shaft; a ring-shaped coil disposed in said closed loop magnetic circuit to develop a voltage at a frequency proportional to the rate of variation of said air gap; a second ring-shaped ferromagnetic member disposed in a side-by-side relationship with said ring-shaped permanent magnet opposite to the first-mentioned ring-shaped ferromagnetic member, and a second ferromagnetic circular member rotatable with and axially spaced from the first-mentioned ferromagnetic circular member and disposed inside said second ring-shaped ferromagnetic member to form a second air gap therebetween, wherein said coil is located between said first and second ferromagnetic circular members.

Claim 7

A speed detector as claimed in claim 3, wherein said ferromagnetic circular member is connected to said rotary shaft.

Claim 8

A speed detector as claimed in claim 4 or 3, wherein said second ring-shaped ferromagnetic member is internally formed with a plurality of teeth axially aligned with the teeth of said first ring-shaped ferromagnetic member, and wherein said second ferromagnetic circular member is externally formed with a plurality of teeth axially aligned with the teeth of said first ferromagnetic circular member.

Claim 9

A speed detector as claimed in claim 4 or 5, further comprising a second ring-shaped permanent magnet magnetized in the axial direction of said rotary shaft but opposite to the direction of magnetization of the first-mentioned permanent magnet and disposed so that said ring-shaped ferromagnetic member is sandwiched between said first and second ring-shaped permanent magnets to form a second closed loop magnetic circuit which said ferromagnetic members, and a second coil disposed in said second magnetic circuit to develop a voltage at a frequency proportional to the rate of variation of said air gap, the first and second coils being connected in a series circuit so that the voltages respectively developed in said coils are constructively added.

Claim 10

A speed detector as claimed in claim 4 or 3, further comprising means for eliminating a higher frequency component of said voltage and means for shaping the waveform of the output of said eliminating means into a rectangular pulse.

Claim 11

A sewing machine having a rotary shaft for reciprocating a needle, comprising: a ring-shaped permanent magnet uniformly magnetized in a direction parallel to the axis of said rotary shaft; a ring-shaped, internally toothed ferromagnetic member; an externally toothed ferromagnetic circular member disposed inside of said ring-shaped ferromagnetic member with a spacing therefrom to form an air gap between the teeth of each said ferromagnetic member and the teeth of the other ferromagnetic member, said ferromagnetic members forming a closed loop magnetic circuit with said permanent magnet and disposed rotatably with respect to each other by revolution of said rotary shaft so that said air gap varies periodically at a rate proportional to the speed of revolution of said rotary shaft; a ring-shaped coil disposed in said closed loop magnetic circuit to develop a voltage at a frequency proportional to the rate of variation of said air gap; a second ring-shaped ferromagnetic member disposed in a side-by-side relationship with said ring-shaped permanent magnet opposite to the first-mentioned ring-shaped ferromagnetic member, and a second ferromagnetic circular member rotatable with and spaced from the first-mentioned ferromagnetic circular member and disposed inside said second ring-shaped ferromagnetic member to form a second air gap therebetween, wherein said coil is located between said first and second ferromagnetic circular members.

Claim 12

A sewing machine having a rotary shaft for reciprocating a needle, comprising: a ring-shaped permanent magnet uniformly magnetized in a direction parallel to the axis of said rotary shaft; a ring-shaped, internally toothed ferromagnetic member; an externally toothed ferromagnetic circular member disposed inside of said ring-shaped ferromagnetic member with a spacing therefrom to form an air gap between the teeth of each said ferromagnetic member and the teeth of the other ferromagnetic member, said ferromagnetic members forming a closed loop magnetic circuit with said permanent magnet and disposed rotatably with respect to each other by revolution of said rotary shaft so that said air gap varies periodically at a rate proportional to the speed of revolution of said rotary shaft; a ring-shaped coil disposed in said closed loop magnetic circuit to develop a voltage at a frequency proportional to the rate of variation of said air gap; a second ring-shaped ferromagnetic member disposed in a side-by-side relationship with said ring-shaped permanent magnet opposite to the first-mentioned ring-shaped ferromagnetic member, and a second ferromagnetic circular member rotatable with and spaced from the first-mentioned ferromagnetic circular member and disposed inside said second ring-shaped ferromagnetic member to form a second air gap therebetween, wherein said coil is located between said first and second ferromagnetic circular members.

Claim 13

A sewing machine as claimed in claim 8, wherein said ferromagnetic circular member is connected to said rotary shaft.

Claim 14

A sewing machine as claimed in claim 8, wherein said second ring-shaped ferromagnetic member is internally formed with a plurality of teeth axially aligned with the teeth of said first ring-shaped ferromagnetic member, and wherein said second ferromagnetic circular member is externally formed with a plurality of teeth axially aligned with the teeth of said first ferromagnetic circular member.

Claim 15

A sewing machine as claimed in claim 9 or 8, further comprising a second ring-shaped permanent magnet magnetized in the axial direction of said rotary shaft but opposite to the direction of magnetization of the first-mentioned permanent magnet and disposed so that said ring-shaped ferromagnetic member is sandwiched between said first and second ring-shaped permanent magnets to form a second closed loop magnetic circuit with said ferromagnetic members, and a second coil disposed in said second magnetic circuit to develop a voltage at a frequency proportional to the rate of variation of said air gap, the first and second coils being connected in a series circuit so that the voltages respectively developed in said coils are constructively added.

Claim 16

A sewing machine as claimed in claim 9 or 8, further comprising means for eliminating a higher frequency component of said voltage and means for shaping the waveform of the output of said eliminating means into a rectangular pulse.