Patent GB-947443-A (GB)
Title: Improvements in needle positioning mechanism for a sewing machine
IPC: D05B69/22
Filed: 1962-02-20
Abstract: 947,443. Controlling clutches &c. AMERICAN SAFETY TABLE CO. Inc. Feb. 20, 1962 [Feb. 21, 1961], No. 6565/62. Heading F2L. [Also in Division D1] A sewing machine 20, Fig. 3, is adapted to be stopped with its needle either fully raised or fully lowered. The driving pulley 21 of the machine is connected by a belt 25 to a pulley 26 on a shaft 27. A pulley 29 on the latter is connected by a belt 30 to a pulley 31 driven by motor means 32 through a centrifugal clutch 33 so arranged as to disconnect pulley 31 when the speed of the driving means falls below a predetermined value. Shaft 27 is adapted to be driven, when pulley 31 is disconnected, by a motor 36 via an overrun clutch. The arrangement is such that the sewing machine is normaly driven at 6000 r.p.m. by the motor means 32, and that when the speed drops to 360 r.p.m. pulley 31 is disconnected and motor 36 drives the machine at 360 r.p.m. till the machine is stopped in the predetermined position by brake means associated with motor 36. The motor of the driving means 32 is housed in a casing 83, Fig. 6, and drives a flywheel 79 formed with an annular rib 80. A boss 84 on casing 83 slidably journals a sleeve 89 in which is journalled a shaft 93 to one end of which is fixed a wheel 97 provided with opposed friction rings 98, 99. The other end of shaft 93 is fixed to a sleeve 100 rigid with a hub member 101 from which project two diametrically-opposed pins 105. Slidable on each pin 105 is an arcuate friction shoe 106, the shoes being drawn together by a pair of springs 108. The pulley 31 is journalled on sleeve 100 and is formed with a cylindrical extension 103 surrounding the shoes 106. A pair of diametrically-opposed studs 95 project from sleeve 89 through slots 94 in boss 84, and are engaged by the forked upper end of a linkage 34 connected to a treadle 35. Depression of the latter moves sleeve 89 to engage ring 98 with rib 80 for driving shaft 93 at high speed, when the shoes move outwardly to engage extension 103 for driving pulley 31. On release of treadle 35 ring 99 engages an annular rib 87 of casing 83 to brake shaft 93, which becomes uncoupled from pulley 31 when the sleeves 106 move inwards. Motor 36 drives a shaft 52, Fig. 4, via reduction gearing 51. Mounted on shaft 52 is one half 40b of an overrun clutch, the other half 40a of which is mounted on shaft 27 which is journalled in a casing 28. A wheel 62 fired to shaft 27 is embraced by a pair of brake shoes 65, Fig. 5, carried by arms 64 which are pivoted at 67 to casing 28 and are connected by pivotal links 70 to a U-shaped member 72 which also carries rollers 73 engaged with vertical surfaces of casing 28. Member 72 is connected to the plunger 76 of a solenoid 77, energization of which moves plunger 76 downwardly, against spring bias, to engage shoes 65 with wheels 62. The pulley 21 of the sewing machine carries a reflective strip 37 which is adapted, in the top and bottom positions respectively of the needle, to co-operate with sensing means 38a and 38b. Means 38a include a lamp 109, Fig. 9, and a photo-electric cell 110, the latter receiving light from lamp 109 reflected from strip 37 when the needle is raised. Means 38b includes a lamp 124 and photo-electric cell 125. The lamps are supplied with A.C. via a transformer 123. The remainder of the control gear is supplied with D.C. via a rectifier 126. A main switch 127 is so coupled to the treadle 35 as to be open when the latter is fully depressed, and to close when the treadle is raised sufficiently to disengage clutch member 97 from the driving rib 80 but before member 97 engages the braking rib 87. When switch 127 is open, a capacitor 163 is charged to mains voltage via a resistor 128. When switch 127 is closed, the down photo-cell 125 is normally energized via the solenoid 134 of a relay 135 and movable contact 151 of a relay 143, the current being insufficient to operate relay 135 owing to the high speed of reflector 37, and motor 36 is energized via the movable contact 158 of relay 135. When the speed has been reduced sufficiently for the photo-cell 125 to be activated, relay 135 operates to shift its contacts 157, 158, 159, whereby motor 36 is de-energized and is shunted by resistor 168 for dynamic braking, while solenoid 77 is energized, initially at full mains voltage from capacitor 163 and then at reduced voltage via resistor 128, to stop the motor pulley 21. To stop the machine with the needle in the up position, switch 141 is temporarily closed, whereby, on closing of switch 127, coil 146 is energized to operate relay 143 to shift contact 147 to the holding position for coil 146 and to shift contact 151 to energize the " up " photo-cell 110. On opening of switch 127, coil 146 is de-energized to condition the machine for stopping in the down position. For making single stitches, treadle 35 may be depressed sufficiently to close switch 127 but without engaging member 97 with rib 80. The machine will then be driven to the " down " position by motor 36. The treadle is then released, switch 141 is closed, and the treadle is again partly depressed, when motor 36 will drive the machine to the " up " position. In a modification, Figs. 11 and 12, shaft 27 is coupled directly to the sewing machine main shaft and the brake disc 62 is provided with a magnet 172 adapted to co-operate with two fixed switches 175 and 176 for determining the down and up positions respectively of the needle. When switch 179 is closed, upon release of the treadle 35, motor 36 is energized via contact 181 of switch 180, contact 185 of relay 183 and the contact 198 of switch 175, till contact 198 is shifted by magnet 172 to alternative fixed contacts 200. Motor 36 is thereby deenergized to stop the machine. If switch 180 is shifted to contact 182, on closing of switch 179 coil 184 of relay 183 is energized to open contact 185 and to close contacts 186 and 187. Motor 36 is thereby energized via switch 176 until the movable contact 199 is shifted by magnet 172 to the fixed contacts 202, whereby motor 36 and relay 183 are de-energized, and brake coil 191 is energized to stop the machine.