Patent GB-1517296-A (GB)
Title: Sewing machines
IPC: D05B21/00
Filed: 1975-08-12
Abstract: 1517296 Sewing machine UNION SPECIAL CORP 12 Aug 1975 [12 Aug 1974 14 Jan 1975] 33498/75 Heading D1G An automatic sewing machine comprises a sewing needle, a work holder for holding a workpiece during sewing, a storage element having a plurality of randomly addressible storage locations for directing sewing of the workpiece, a control system adapted to read these instructions and produce output signals representing said instructions and means responsive to the signals and arranged to direct movement of the work holder to produce a predetermined sewing sequence.  The work clamp 16 comprises an extendable arm 70 carrying a lower clamp jaw 198 and an upper member 202 pivoted at 204 to the arm 70 and carrying the upper clamp jaw 220. A spring 206 biasses the jaws together; the clamp is opened by a cable. 218 operated by a pneumatic cylinder (216, Fig. 1 not shown). The cable 218 passes around a cable tension sensing assembly (222, Fig. 1 not shown) which provides a signal indicating whether or not the work clamp is closed. Triangular rails 194 are engaged by rollers 172-178 carried on an arm 52 (Fig. 10) pivoted at 68 to a fixed plate 46, two of the rollers (176, Fig. 6 not shown) being, carried  levers (180, 182) urged apart by a spring (188). The The work arm is rotated by a cable 36 and extended by a cable 34 entrained by respective stepping motors 20, 18 controlled by a logic circuitry. (Figs. 8, 13 not shown) including a randomly addressable programmable read only memory. Cable 36 extends from a fixed anchorage 58 around pulley 56 rotatably mounted beneath pivoting arm 52, around pulley 28 on stepping motor 20, around pulley 54 on a 'homing' device 55, around pulley 53 journalled on the fixed plate 46 and around a second pulley 50 rotatably mounted beneath arm 52. Rotation of motor pulley 28 thus swings arm 52 about its pivot 68. Cable 34 is similarly entrained about its motor pulley 30 and pulley 86 of its limit and homing device 88. The ends of the cable are anchored to the extendable arm 70 at 72 and 94, after passing around pulleys 74, 90 rotatably mounted on the fixed plate 46; operation of the stepping motor thus extending arm 70 radially of pivot 68. The homing and limit assemblies 55, 88 function to position the work clamp at a predetermined location at the start or end of sewing and to an indication, i.e. a contact closure, to indicate that the work holder is being moved beyond predetermined limits, and provide physical resistance to movement beyond the limits. Device 88 comprises a shaft 108 secured to cable pulley 86 and carrying a trigger 140 and a homing disc 160. The former moves between two limit switch assemblies (134, 136, Fig. 9 not shown) to close the contacts thereof if the motors drive the work holder beyond the allowed range of movement and into potential contact with the needle, such closing preventing further stepping of the motor until its direction of travel is reversed. Back-up screws (158) provide mechanical stops for the trigger in case of electrical failure, the stops being positioned one motor step beyond contact actuation. The homing disc 160 is secured to the shaft 108 and its edge, which is apertured (at 168) passes between the arms of an optical sensor 162 comprising a light emitting diode and a photoresistor. The device detects the presence or absence of the aperture and provides a signal to the logic circuitry to enable the work holder to be precisely positioned for the start of sewing or for the operation of work cutting devices. The shaft 108 is adjustably connected to pulley 86 by a lever and screw device 144, 146, 150, 152 (and 148). Presser foot Fig. 2. The needle is provided with a work stripper 272 loaded by a spring 274 connected to the needle bar.  Synchroniser. To ensure that the work is moved only when the needle is out of the work a synchroniser (Fig. 7) is provided and includes a slip ring assembly 224 attached to the machine hand wheel 24. Four brushes 230, 232, 234, 236 respectively co-operate with the three slip rings 244, 246, 248 and supply current to the slip ring; the signals therefrom being utilised to (a) run the machine at a selected fast or slow speed, (b) actuate a thread cutter and tension release and (c) stop the machine with the needle up. The synchroniser has a reflective ring 262 gapped at 270 and angularly positionable with respect to a scale 268 on a cover 266. Light emitted from a photo reflective transducer 256 strikes the ring 262 and is reflected back to the transducer except when the gap 270 is in register, when the signal change indicates the beginning of a time period when the work clamp may be moved as the needle is out of the work. Presser feet. A spring (274, Fig. 12 not shown) is secured at one end to the needle bar and carries a stripper (272) at the other end. The stripper surrounds the needle and contacts the work.