Patent GB-937339-A (GB)
Title: Improvements in or relating to sewing machines
IPC: D05B27/08
Filed: 1962-05-16
Abstract: 937,339. Sewing-machines. G. M. PFAFF A.G. May 16, 1962 [July 20, 1961], No. 1371/62. Class 112. A sewing-machine having main and auxiliary feed dogs each having stitch length setting means the positions of which are determined by setting shafts, one for each feed dog, for the adjustment of the differential feed, is characterized by the provision of a coupling spring effecting engagement of abutments connected one with each of the shafts. Feed advance movements for feed bars 36, 39 carrying a main dog 35 and an auxiliary dog 38 respectively are derived from eccentrics 28 and 29 respectively. The eccentric strap 30 is pivotally connected at 45 to both a link 46 pivoted at 48 to a crank 49 on the main dog setting shaft 2 and to a link 47 pivoted at 50 to a crank on. a hollow shaft 32 which carries a lever 34 connected to the main feed bar 36. The eccentric rod 31 is connected at 52 to both a link 53 pivoted at 55 to a crank 56 on the auxiliary dog setting shaft 3 and to a link 54 pivoted at 57 to a crank 58 on a shaft 33 journalled in the shaft 32 and carrying a lever 37 connected to the auxiliary feed bar 39. When the members 48 and 50, and 55, 57 are respectively coaxial then the feed dogs receive no feed advance. Rotation of setting shafts 2 and 3 displace the members and the dogs receive feed advance movements. The movements of the setting shafts are derived from a cam groove 13 in a rotatable setting disc 14. In one embodiment (Fig. 2), the groove is engaged by one end 12 of a first order lever the other end of which is connected to one arm of a two-armed lever 8 secured to the main dog-setting shaft 2. A spring 16 biases the shaft to maintain the lever end 12 against the cam groove at A. The other arm of lever 8 is connected at 18 to a bridge 17 surrounding the auxiliary setting shaft 3 and biased by a coupling spring 23, secured to that shaft, in a direction to cause one arm of an abutment 21, carried on the shaft 3, to contact a setting screw 20 on the bridge. In this arrangement the force of only the spring 16 has to be overcome when depressing the tack bar 24 to reverse the feeding direction. Setting screws 19 and 20 may be adjusted by turning backward and forward respectively to cause the auxiliary feed dog to effect the greater feeding movement, to shirr the material, the reverse movement of the screws providing for stretching the material. If a predetermined maximum feed length movement is temporarily desired for the feed dog, screw 19 is turned back to adjust the magnitude of feeding and a pedal is depressed to rotate a crank 25 on the shaft 3. On release of the pedal the coupling spring 23 returns the shafts to the original condition. In a second embodiment (see Fig. 3), the main dog setting shaft 102 is biased by a spring 116, and the shaft 102 is connected to the auxiliary dog setting shaft 103 by a coupling spring 123. The shaft 102 is connected by a rod 109 to a hollow shaft 133 journalled on a shaft 111 and carrying both a projection 112 which enters the cam groove in the rotatable setting disc 14 (not shown in Fig. 3), and a counter abutment number 132. Shaft 103 is connected by a rod 128 to the shaft 111 on which is disposed an abutment 129 disposed between two straps 134 connected by a spring 135 and carried on a member 134 rotatably mounted on the hollow shaft 133 and provided with screws 119, 120 which correspond in function to the screws 19, 20.