Patent GB-930019-A (GB)
Title: Braking mechanism for sewing machine
IPC: D05B69/22
Filed: 1961-04-06
Abstract: 930,019. Sewing-machines. NECCHI S.p.A. April 6, 1961 [April 30, 1960], No. 12370/61. Class 112. [Also in Groups XXIV and XXXV] A sewing-machine is provided with means adapted to stop the main shaft in a predetermined angular position and comprising an electromagnetic clutch and an electromagnetic brake alternatively connectible by control means to a source of energy, a relay being arranged to be energized when the brake winding is energized and being adapted to switch the brake winding into a circuit fed by the same source of energy, and to switch the clutch winding into a circuit of reduced energization, each circuit containing a contact engageable by a member rotating with the main shaft, and the arrangement being such that when one contact is open the other contact is closed and vice versa, whereby the brake is engaged when the main shaft is in said position. As shown, a pulley 5 on the main shaft 6 of a sewing-machine 7 is connected by a belt 8 to a pulley 4 driven by a motor 1. The motor shaft 2 carries a flywheel 9 to which is fixed a disc 10 enclosing a space containing a clutch disc 11 rigid with a shaft 3 carrying pulley 4. Plates 13 and 14, rigid with the motor casing, enclose a space containing a brake disc 12 rigid with shaft 3. Said spaces are provided with magnetic powder held near the peripheries of the discs by intermeshing ribs 15. Disc 11 is surrounded by a coil 17 which, when progressively energized, effects a coupling of progressively increasing rigidity between shaft 2 and disc 11 for transmitting drive of variable speed to shaft 3. A coil 18 surrounding disc 12 when energized effects braking action on shaft 3. A disc 55 fixed on shaft 6 has a non-conducting segment 62 and a conducting segment 63, and is engaged by diametrically opposed brushes 64 and 66. A similar disc 56 has a conducting and a non-conducting segment 59 and 60, respectively, and is engaged by diametrically opposed brushes 65 and 67. Segments 59 and 63 are connected to a terminal 53. The arrangement is such that when segments 59 and 62 engage the brushes 65 and 64, the needle is in the lowered position, and when the segments 59 and 62 engage the brushes 67 and 66, the needle is in the raised position. A two-pole two-way switch 58 is so arranged that either brush 64 or brush 66 can be connected via a resistance 54 to a terminal 23 of the clutch coil 17, and either brush 65 or brush 67 can be connected to a terminal 28 of the brake coil 18. The other terminals 24 and 29 of the respective coils 17 and 18 are connected to one terminal 25 of a rectifier 19. A commutator disc 48 on shaft 6 is provided with conducting segments 49 and insulating segments 50, and is engaged by two brushes 51 and a brush 51<SP>1</SP>, the arrangement being such that the brushes 51 are electrically connected and disconnected from one another at a rate proportional to the speed of shaft 6, and brush 51<SP>1</SP> is alternately connected to the respective brushes 51. Brush 51<SP>1</SP> is connected via a condenser 52 to the terminal 25 of rectifier 19. One brush 51 is directly connected to the other terminal 21 of rectifier 19. The other brush 51 is connected to terminal 25 via the coil 44 of a relay 43, coil 44 being shunted by a condenser 45. The arrangement is such that when shaft 6 runs above a predetermined speed, coil 44 is sufficiently energized to shift a switch member 41 from a contact 47 connected to terminal 53, to a contact 42 connected to terminal 28. The machine is controlled by a treadle 32 arranged to close alternatively either a switch 22 connected between terminals 21 and 23, or a switch 26 connected between terminal 21 and the switch member 41. Closing of switch 22 energizes clutch coil 17 to drive the machine, the speed of which can be regulated by a variable resistance 33 associated with switch 22 and actuated by treadle 32. Closing of switch 26, when the machine speed is above the predetermined value, energizes the brake coil 18. When the speed falls below said value, switch member 41 shifts to contact 47, and coil 18 is then partly energized via a resistance 68 connected between terminals 28 and 53, while shaft 6 rotates slowly, since clutch coil 17 is energized via segment 63 and resistance 54, until the selected brush 65 or 67 engages the segment 59 for fully energizing the brake coil 18 to stop the machine. For emergency stopping, a coil 85 of a relay 84 is energized to open a switch 83 in the main circuit to the clutch coil 17, and to close a switch 82 in an auxiliary circuit comprising the brake coil 18. In a modification, the commutator 48 is dispensed with, the terminals 42 and 47 are interchanged, coil 44 is connected to switch 26 so as to be energized when the latter is closed, and relay 43 is arranged to shift switch-member 41 from contact 42 to contact 47 after the lapse of a predetermined period of time following the energization of coil 44.