GB723595A - Improvements in or relating to thread tension devices - Google Patents

Abstract

723,595. Sewing-machines. BRITISH UNITED SHOE MACHINERY CO., Ltd. (United Shoe Machinery Corporation). Aug. 28, 1953 [Aug. 29, 1952], No. 21705/52. Addition to 630,639. Class 112. In a thread-tensioning device according to the parent Specification, the braking band has an end portion extending more or less tangentially from its turns to be engaged by the member which causes it to grip the brake drum, and the latter member, while thus engaging the end portion of the band, exerts a frictional force lengthwise of it in a direction to assist in the required effect. Modified means are used for holding and adjusting the other end of the band, and provision is made for the application of only a reduced tension during the first stitch-forming cycle on starting (the tension being substantially removed when the machine is at rest) to avoid the possibility of pulling the thread out of the thread-end holder; the full tension is restored during the second cycle. In the form shown in Fig. 5 the brake band 20 surrounding the brake drum 17, which is secured to a spindle 16 rotating in needlebearings under the action of the thread passing over a wheel on the spindle, has one end 43 adjustably secured by means described below and the other end 19 extending tangentially into engagement with a roller 22 carried by the take-up lever 8. The arrangement is such that as the take-up lever moves to set a stitch it deflects the end 19 of the brake band to the left and at the same time exerts a frictional force drawing it downwards, both these actions serving to tighten the band on the drum to increase the thread tension; the second action ensures that the first turn of the band engages the drum to ensure smooth and correct action. When the take-up moves to give up thread the reverse effect occurs, the end of the band being lifted frictionally to disengage the first turn from the drum. The other end 43 of the band is guided in a fork 50 of a member 44 pivotally mounted on one of the bearings of the drum spindle, a screw 52, with lock-nut, being provided for adjustment of the band whereby the thread tension is adjusted. The member 44 is normally held in a position to tighten the brake band by a lever 60 engaging under the end of an arm 56 of the member 44 under the action of a spring 70: when the machine is stopped, the lever 60 is tilted to the position shown by a rod 82 to relieve the stress in the brake band and remove the tension in the thread. In the arrangement shown in Fig. 8 in the position in which the brake band is slackened, the member 84 engaging the end 43 of the band rests on a lever 90 spring-pressed clockwise and connected by a link 116 with a pivoted arm 114 in engagement with a second arm 110 which is moved anti-clockwise when the machine stops and which thus lifts the. arms 114 to the position shown. When the machine is started, the arm 114 is lowered by a spring 126 until stopped by a latch 118 engaging a nose 115 on the arm 114; in this position the member 90 engages the incline of a cam projection 85 on the member 84 so as to tighten the brake band enough to apply a tension less than normal to the thread. On its return from setting the first stitch, the take-up lever engages a nose 124 to draw the latch 115 clear of 114, so that the arm 114 can fall further and restore full tension to the thread by moving the member 90 right under the projection 85. Specification 656,765 also is referred to.