Patent GB-493628-A (GB)
Title: Improvements in or relating to sewing machines
IPC: D05B15/04
Filed: 1937-04-17
Abstract: 493,628. Sewing - machines. BRITISH UNITED SHOE MACHINERY CO., Ltd. (United Shoe Machinery Corporation) April 17, 1937, No. 10992. [Class 112] In a high-speed lock-stitch shoe-sewing machine with a curved hooked needle, similar to that described in Specification 419,726, a measured amount of locking thread is drawn from the thread case for each stitch, and a thread lock on the thread case ensures that only this amount is used in the formation and setting of eacli stitch, the measured length of thread being held yieldingly against movement towards the work so that the locking thread between the thread case and the work is taut and the needle loop slides on it to the proper point before pulling it into the work, thus giving uniform stitch-setting ; the measured length of thread is varied according to the length of stitch by control from the feed mechanism. Means are provided for releasing the needle and locking threads when the machine stops and for pulling off sufficient locking thread to start a new seam before cutting the threads. A thread-cutter having a helical downward movement is provided, its stroke being adjusted in accordance with the workthickness by a connection to the presser-foot ; the cutter is actuated by a one-revolution clutch brought into operation when the machine is stopped, but can be disconnected to avoid actuation if it is necessary to stop the machine before the completion of a seam. Improved presser-foot lifting and locking means are provided, and the presser-foot is automatically lifted after the threads are cut ; the machine also has improved needle guides. The machine is started and stopped by a treadle which brings into operation a low-speed reverse drive in the usual way and also controls the operation of a one-revolution clutch actuating the thread-cutting device. The shoe is presented and guided by hand, instead of being guided automatically ; the feed is arranged to be practically continuous. Feed.-The feed is practically continuous, by alternate feeding movements of the presserfoot 38 and work-support 40 and of the needle 26 while in the. work. The presser-foot and work-support are mounted on a feed-carriage 267, Fig. 9, connected to a lever 269 which is actuated by means of a link 271, crank 273 and frame 277 oscillated by engagement of a pin 281 with a cam on the main shaft 4. The frame 277 is supported by a link from a pin 289 on one limb of a U-shaped yoke 291, pivoted near its base. The needle is carried on a stud 310, Fig. 10, having a threaded bearing engagement with the carriage 267, the stud 310 being oscillated, to produce the feeding movement of the needle relative to the carriage, by a gear sector 295, Fig. 9, operated through an arm 299 and link 301 ; the link 301 is guided by a pin 309 sliding in a forked guide 311 and is pivoted to a frame similar in form and operation to the frame 277 and supported similarly on the other limb of the yoke 291, so that adjustment of the yoke on its pivot produces simultaneous adjustment of the two feeding mechanisms. Governing locking thread.-The locking thread 140, Fig. 19, from the bobbin passes to the outside of the thread-case 32 under a tensioning spring 58 and lies against abutments 44, 46 on the thread-case and in a guide 60. Spring- pressed pivoted cam-shaped grippers 62, 68 normally press the thread against the abutments to hold it positively against movement from the work and from the bobbin respectively while yielding to opposite movements. A thread-measuring finger 42 with a grooved end slides between the abutments 44, 46, to pull off a measured length of thread, the finger engaging the tail of the gripper 68 to release it to allow the thread to be drawn from the bobbin ; the gripper 62 prevents any effect on the stitch already formed. When the finger 42 is retracted, as shown, to allow the needle loop to pass round the thread-case, the measured thread can be drawn through the gripper 62, which keeps it under tension to ensure proper stitch setting, the gripper 68 preventing any more than the measured length from being drawn off. The finger 42 slides in a fixed guide 67, Fig. 10, and its movement comprises two parts, a fixed part carrying it to the point at which the gripper 68 is released and a further adjustable part for measuring the thread. The finger is connected by a link 82 with a link 86 which is free on a shaft 88, Fig. 9, but is pressed downwards against a stop finger on the shaft by a spring 92. The shaft 88 is carried by a yoke 98, mounted on a shaft 100, having a rearwardly-extending arm connected by a link 102 to a lever 104 actuated by a cam on the main shaft 4 to rock the yoke 98 on its shaft 100 and give the finger 42 its fixed movement. The shaft 88 has an arm 108 pivoted at 110 to a link 112 engaging an arcuate slot in a lever 122 which is pivoted at 124 and is also actuated by a cam on the main shaft ; the pin 110 and the slot in the lever 122 are normally coaxial with the shaft 100, so that the arm 108 is not effected by rocking of the yoke 98 or by shifting of the link 112 along the slot to vary the thread-measuring movement of the finger 42 which is produced by oscillation of the shaft 88 in the yoke 98. The movement of the link 112 along the slot in the lever 122 is produced by a carrier 116 fixed in a block 126 pivoted to a lever 128 which is fulcrumed at 130 in a pivotally mounted frame 325 and has a rounded end engaging a recess in a block 132 secured to the frame. The frame 325 is connected by a link 323 to the feed-adjusting yoke 291, so that the length of thread measured off by the finger 42 is varied with the length of stitch, independent adjustment being afforded by a nut on the screwed shank 136 by which the block 132 is fixed. The finger 42 is arranged to be in such a position that the gripper 68 is open when the machine stops, so that thread can be drawn from the bobbin by hand if desired. Governing needle thread.-The take-up comprises an arm 37, Fig. 7, fixed to a shaft 144 and carrying a pulley 148. The thread passes round a tension wheel 146, over a guide pulley 150 and the pulley 148, and then through an intermittent tension device to the looper 34. The latter device comprises a plate 152 slidable on pins 156 under spring pressure to press the thread against a fixed member without deflecting it laterally. The tension is released when the needle passes up through the work by a rod 164, operated by a cam on the shaft 144, engaging the bevelled end of a pin 154 fixed to the plate 152 ; the arrangement is such that the tension is released when the machine stops. Presser-bars, lifting and locking.-The means for locking and releasing the presser-bar is a modification of that described in Specification 288,352, [Class 112]. The presser-foot 38 is fixed to an arm 181, Figs. 6 and 32, pivoted at 174 and actuated by a link 179 lying on a line passing close to the presser-foot, to avoid any tendency to movement owing to looseness in the pivot 174 or elsewhere, and slightly inclined as shown in Fig. 32, so that the feeding movement of the presser-foot to the left tightens its grip. The link 179 is universally jointed to the arm 181 and to a wedge block 176 which co-operates with another wedge 178 with an integral upwardly-extending operating rod; the wedges are contained in a housing 191, and are connected to one another and to the housing by links as shown, lost-motion being allowed at the pivot 227 so that the wedge 178 can unlock the wedge 176 without immediately lifting it. The rod 178 is pressed down by links 180 pivoted to its upper end and to a lever 182 actuated by a spring 184. To raise the presser-foot intermittently, a yoke 195 sliding on the rod 178 and pressed down by a spring 199 has pivoted on it a cam-ended gripping arm 197 with a forked end slidably embracing a square block pivotally carried by a lever 203 which has an arcuate slot in one arm for adjustable engagement with a link 207 connected to a crank 209 actuated by a cam on the main shaft 4 ; actuation of the crank 209 causes the arm 197 to grip the rod 178 and raise it through a predetermined distance, the grip being released on the downward movement by the yoke 195 striking an adjustable stop on the wedge housing 191 so that the downward movement of the presser-foot is completed by the spring 184. The presserfoot is raised after the threads are cut at the end of a seam by a lever 254 engaging a stop screw 262 on the lever 182 and actuated by a link 258 from a cam-operated lever 260. Thread-cutters ; governing threads otherwise than in stitch-forming.-A curved knife 186, Figs. 6 and 29, clamped in a block 229 at the lower end of a slidable and rotatable shaft 190, is given a helical movement to cut both threads below the surface of the work during the stopping of the machine; the path of the knife is varied according to the thickness of the work by a connection to the presser-foot. Rotation of the shaft 190 is derived from a cam 212 by means of a lever 206, pivoted at 208, a link 204, a sliding rack 202, Fig. 10, and a lever 196 which has a toothed segment at each end, one engaging the rack 202 and the other a toothed sector slidably engaged by a squared upper part of the shaft 190. The vertical movement of the shaft 190 is also derived from the link 204 through a link 228, Fig. 9, a lever 226, a shaft 224 and a lever 222 which has an arcuate slot adjustably engaged by a link 218 pivoted to a yoke on the shaft 190. Adjustment of the link 218 along the slot in the lever 222, which is normally in such a position that this adjustment does not move the shaft 190 so that the position of rest of the cutter is fixed, is effected by a link 529 pivoted to an arm 230 fixed to a shaft 232 which has another arm supporting a feeler link 188 formed with a slotted end engaging a pin 189 on the presser-foot arm 181. The link 188 is held down while the machine is running, to allow free operation of the p