Patent GB-851464-A (GB)
Title: Lock stitch sewing machine
IPC: D05B57/14
Filed: 1958-09-08
Abstract: 851,464. Sewing machines. SINGER MANUFACTURING CO. Sept. 8, 1958 [Sept. 19, 1957], No. 28700/58. Class 112 Stitch-forming devices, feed by clamps. In a cyclically-operated sewing machine the arrangement is such that between the first and second penetrations of the needle in any cycle, sufficient' thread is pulled through the needle eye and stored in the looptaker to provide the under-thread of lockstitches formed in the seam or tack produced in the cycle. As shown, the machine is generally of conventional form, having a cam wheel 33 provided with a frontal cam groove 38 engaged with a lever 36 controlling the transverse movements of a workclamp 30, a rear cam groove (not shown) engaged with a lever 37 controlling the longitudinal movements of the work-clamp, and a pair of diametrically opposed cam lugs 60 adapted to release a stop-motion frame 52 at the respective ends of successive stitching cycles, the wheel being arranged to control two cycles for each revolution thereof. A shuttle, which comprises a body 26 journalled in a fixed race 27, is driven by a member 25 carried by one end of a shaft 24 oscillatably driven via a two-armed lever 19, 21 and a pitman 18 from the arm shaft 14. Body 26 is formed with a central, hollow boss 72 on which is freely journalled the base 76 of a thread container, the boss being held thereon by a jib 78. The outer face of base 76 is rendered cup-shaped by a peripheral flange comprising a wide portion 80 separated by gaps 82, 83 from a narrow portion 81. A face plate 88, slidable within said flange, carries a pin 85 which is acted upon by a spring 87 to bias plate 88 against base 76. A pin 89 prevents relative rotation between base 76 and plate 88, and a finger 90 provided on the latter is disposed between fixed abutments 91 to prevent rotation of plate 88. A leaf spring 94, secured by screws 93 in a vertical slot 92 formed in plate 88, normally engages base 76. Shaft 24 is formed at the shuttle end with an axial bore slidably housing a rod 101 the outer end of which lies adjacent pin 85, and to which is fixed a finger 102. A pin 104 projects radially from rod 101 through a longitudinal slot 103 in shaft 24, and is disposed within the forked end of a lug 107 fixed to a shaft 108. The latter is slidable both in a fixed bearing 109, and also against the bias of a spring 114 in an axial bore in the end of a rod 111 pivoted to a member 115 projecting from one arm of a bell-crank lever 116, the other arm of which is biased towards cam wheel 33 by a spring 118. The arrangement is such that a follower pin 119 on lever 116 is engaged by a cam lug 120 when the shuttle is engaging the needle thread loop on the first penetration of the needle in each stitching cycle, whereby rod 101 engages pin 85 to separate plate 88 from base 76, and finger 102 engages the shuttle body 26 to clamp the free end of the needle thread there against. In consequence, during the first loop-taking movement of the shuttle, the needle thread loop does not pass around the shuttle but one limb passes through the gap opened between base 76 and plate 88, enters the vertical slot 92 in the latter and passes through the gaps 82, 83. The cam lug 120 then leaves the follower pin 119, whereby rod 101 is retracted to release plate 88 and the thread end, when spring 94 clamps the upper end of the thread disposed in slot 92 against base 76. The thread contained within slot 92 then serves as the underthread for the lock stitches in the tack. Thread control. In order to prevent the thread take-up 15 from withdrawing all the thread from the thread container and for supplying to the latter the exact amount of under-thread required for a particular tack, a thread-metering device is provided, the device being actuated by the work clamp-opening mechanism. A vertical rod 131, slidable in the machine head, is lifted by means of a lever 134 and chain 135, and carries a lug 132 underlying a pin 133 on the upper jaw of the work clamp 30. A lug 136, fixed to the upper end of rod 131 journals a horizontal arm of pull-off lever 139. A downwardly-extending arm 142 of the latter ends in a loop 143 disposed between fixed thread guides 144, 145, and another horizontal arm 147 is disposed beneath a horizontal portion of a fixed post 148. A spring 149 acts on arm 147 to bias loop 143 towards the machine. A screw 150, passing through post 148 and abutting arm 147, serves to swing eye 143 outwardly when rod 131 is raised for opening clamp 30. Thread passes from a tensioner 157 through the take-up 15, guide 144, loop 143 and guide 145 to the needle 17. The tensioner 157 is adapted to be opened, when the machine stops, via a rod 158 actuated by the cam wheel 33. When rod 131 is raised, an abutment thereon actuates a lever 156 on the needle bar 16 to release a leaf spring 155 mounted on the end of the latter to nip the thread. This arrangement ensures that lever 139 draws thread from the supply and not from the needle. The amount of metered thread is determined by adjusting the screw 150. To ensure that the take-up 15 will draw the excess thread from the shuttle on its first movement in any cycle, a thread nipper 162 is adapted to be actuated via a cam lug 120 during the interval between the first and second needle penetrations of each cycle. It is stated that the thread pull-off may, alternatively, be actuated by any suitable cam connection operative, for instance, during the first downstroke of the needle and before loop seizure by the shuttle. Threads, cutting. The upper and lower threads are severed at the end of a cycle by a pair of knives (not shown) rotatable with a gear segment 64 which meshes with a rack 63 carried by a slide rod 62 pivoted to a bell-crank lever 61 adapted to be operated at the end of a cycle by the stop-motion frame 52. Spaced fingers 67 on rod 62 embrace one arm of a knife control lever 65 the other arm of which is engaged with a cam groove 66 in the cam wheel 33, and the arrangement is such that the knives are brought into position for cutting the thread as a cycle nears an end, while the bellcrank lever 61 is carried out of register with frame 52 for most of the cycle to prevent cutting of the threads if the machine is accidentally stopped before the end of the cycle.