Patent GB-1239980-A (GB)
Title: Feed guide for sheet material
IPC: D05B35/10
Filed: 1968-07-31
Abstract: 1,239,980. Sewing machines. IVANHOE RESEARCH CORP. 31 July, 1968 [8 Aug., 1967], No. 36638/68. Heading DIG. A sewing machine 1 has a needle 2 cooperating with lock stitch looptaker, and is provided with conventional feed dogs. The presser bar 53 rigidly carries a disc 5 provided with an axial hole 6 for passage of the needle 2. A ring 7, journalled on disc 5, is provided peripherally with a gear 8 and on its under surface with a friction ring (9) Fig. 4 (not shown) adapted to engage the workpiece 36. Gear 8 is coupled by gearing 12, 21, 20 to the shaft of a servo-motor 18. A slot 23, formed radially in disc 5, slidably receives a finger piece 23 spring-biased inwardly and rigid with a contrast plate 27 which is adapted to be resiliently forced under the edges of workpiece 36 and which has a reflectivity substantially different from that of workpiece 36. One end 29 of a fibrous optical cable 30 is received in a hole 28 formed in disc 5 closely ahead of the stitch-forming point. The fibres of cable 30 are split at the other end into two branches 32 and 33, the ends of which are respectively positioned adjacent a photo cell 37 and lamp 34. Light from lamp 34 is projected as a spot 35 on plate 27 and workpiece 36, the edge of the latter normally bisecting spot 35, and reflected light from which is projected on to photocell 37. A cell 38, Fig. 6, feeds a circuit 39 containing a potentiometer 40, the tapping from which is connected via photocell 37 to the base of a transistor 41. A circuit 42 is connected via a resistance 43 to the collector of transistor 41. Photocell 37 thereby controls the collector-emitter current of transistor 41. A line 44 is connected to one input terminal of a differential amplifier 45 and to a point in circuit 42 between resistance 43 and transistor 41. A line 48 is connected between the other input terminal of amplifier 45 and the tapping of a potentiometer 47 in a circuit 46. Amplifier 45 amplifies on a DC signal the difference between the voltage of lines 44 and 48. The amplified DC signals is passed into a chopper 56 which converts this signal into a square wave AC signal, which, on being amplified is in amplifier 57, is passed to the control phase 50 of the servo motor 18 having a reference or drive phase. When a positive signal is applied to amplifier 45, the control phase is 90‹ out of phase with the drive phase and motor 18 rotates in one direction. When a negative signal is applied to amplifier 45, the control phase is 270‹ out of phase with the drive phase and motor 18 rotates in the opposite direction. In use, after workpiece 36 has been positioned under disc 5, end 29 is adjusted so that the edge of workpiece 36 bisects spot 35, and the potentiometers 40, 47 are so adjusted that equal voltages are applied to amplifier 45 via lines 44 and 48, and stitching is then commenced. If the line of stitching either advances towards or recedes from the edge of workpiece 36, the amount of light reflected from spot 35 will vary, whereby motor 18 turns in one direction or the other to restore the line of stitching to its original distance from said edge, turning of the workpiece occurring when the feed dogs are disengaged from disc 5.