| 摘要 |
639,515. Sewing-machines. SINGER MANUFACTURING CO. Aug. 11, 1948, No. 21160. Convention date, April 5. [Class 112] Presser-bars ; feed by presserfeet :-The pressure applied to the presser mechanism is varied in response to variations in speed of a shaft of the machine, in order tc avoid the effects' of inertia at high speed, especially in a machine having alternating presser-bars one of which is used to feed the work, without requiring heavy pressure at low speeds with consequent possibility of damage to the work and other undesirable effects. In the machine shown a centrifugal device on the main shaft applies additional load to a leaf-spring which acts on the presser-bar and feed-bar. The spring 40 rests at one end on a fixed bracket 41 and at the other on the head of a screw depending from a stud at the middle of a lever 19 of inverted T-form, of which the forward arm is pivoted to the feed-bar 17 and the rearward arm is connected by a vertical link to a collar on the presserbar 13 and by a horizontal link to a part of the machine frame ; the spring is stressed by a rod 45 screwed into a bushing 46 in the machine arm. An auxiliary leaf-spring 47 rests near its left-hand end on the spring 40 and at the other end on the head of a link 48 carried by a lever 50; the bushing 46 is adjusted into contact with the spring 47 to act as a fulcrum. The other end of the lever is engaged between a flange 52a integral with a sleeve 52, slidable on the main shaft 5, and a thrust bearing 53 on the sleeve. A collar 55 fixed on the shaft carries two weights 63 pivoted at 58 to lugs on it and provided with tails 60 in contact with pins sliding in the collar and engaging the ends of the sleeve 52. As the shaft rotates the weights move away from the shaft under centrifugal force and move the sleeve 53 along the shaft, against the action of a spring 66, to lift the right-hand end of the spring 47 and thus apply additional pressure to the left-hand end of the spring 40. The alternate lifting of the presser-bar and feed-bar is produced by an eccentric 20 on the shaft 5, and pitman 22 through arms 23, 26 on a rocking sleeve 24, the latter arm being linked to the upward limb of the T-lever 19. The feed movement of the bar 17 is derived from an adjustable eccentric 21 and pitman 33 through arms 34, 36 on a rock-shaft within the sleeve 24, the lower end of the arm 36 being linked to the bar 17. |
