Patent GB-872010-A (GB)
Title: Improvements in sewing machines
IPC: D05B3/06
Filed: 1959-01-29
Abstract: 872,010. Sewing machines. SINGER MANUFACTURING CO. Jan. 29, 1959 [Feb. 14, 1958], No. 3299/59. Class 112 A sewing machine comprises a thread trimming mechanism effective to sever the needle thread, a thread wiper disposed to act upon the needle thread, mechanism for actuating in sequence the thread trimmer and thread wiper and a thread tensioning device acted upon by cam means operatively associated with said mechanism. The sewing machine Fig. 1 is fitted with a work clamp having a frame 15 to which is affixed a lower jaw plate 16, opposed by a pair of upper jaw members 17 carried in frame 15 and biased downwards by leaf springs 18. So that the work clamp may be opened, each of the upper jaw members is provided with a pin 19 which overlies a bracket 20 attached at the lower end of a slide rod 21, journalled vertically in the bracket arm 13 of the machine. Clamped to the slide rod is a guide block 22 which is connected by rocker arm 28, rocker shaft 29, link 31 and lever 32 to a treadle to facilitate opening of the clamp by the machine operator. Pivotally mounted beneath the throat plate 40 on an axle 42 Fig. 4A are a pair of thread engaging and cutting fingers 44 and 45 having cutting edges 46 and 47 respectively. Fixed on the axle 42 is a gear segment 49 meshing with a rack 50 which is connected to the clamp lifting lever 32, through a linkage 51, 52, 53, 55, so that movement of lever 32 rotates the fingers 44 and 45. The machine is also fitted with a thread wiper 60 Fig. 4B mounted on arm 61 pivoted at 62 to a support block 63 on the bracket arm 13, and connected to the slide rod bracket 20 by a second arm 64. Thus when the work clamp is opened by bracket 20, the thread wiper 60 is moved beneath and across the path of the needle. The machine is also fitted with a pair of thread guides 70, 71 through which the needle thread is directed to a friction disc tension device 72 shown in detail in Fig. 4. The device comprises a base member 73 held in bracket arm 13 by means of a set screw 74. Mounted on a stud 76 is a check spring 84. The stud extends from the base member and carries a pair of friction discs 78 holding the needle thread and biased against the base member by a spring 79 and pressure slate 80. A plunger 88 disposed in a bore 89 in the bracket arm engages a tension release pin 87 at one extremity and at the other extremity bears against the guide block 22. The guide block is formed with cam means comprising two notches 90, 91 with a land 92 between them, all in the path of the plunger 88. When the work clamp is in the closed position, the plunger 88 is engaged in notch 90 so permitting the tension coil spring to bias the friction discs 78 together. As opening of the work clamp is initiated the plunger 88 being engaged by land 92 as in Fig. 4 will release the thread tension by acting against the coil spring 79. Figs. 4A, 4B show the relative positions of the thread trimmer and the thread wiper at this position of the cam means. The initial release of the thread tension is to provide relaxation of the check spring so that it will withdraw an additional amount of thread from the supply and Figs. 4A, 4B show that the needle thread N and bobbin thread B have not yet been severed so that the thread can be withdrawn without the possibility of a severed thread being drawn back through the eye of the needle. Continued opening of the work clamp will result in the plunger entering notch 91, again establishing the coil spring pressure on the friction discs 78, also the threads B and N are severed and the thread wiper is swung under and across the needle to wipe the severed threads from the work. The purpose of re-establishing the tension is to prevent the thread wiper from drawing thread from the supply. Finally when the work clamp is completely open the plunger 88 will be engaged by the guide block 22 beyond the notch 91, and the tension device will be released for the second time and remain so while the work clamp remains open, so that the machine may if needed be re-threaded.