Patent GB-934739-A (GB)
Title: Improvements in or relating to a device for changing the ratio and the direction of transmission between a driving shaft and a driven shaft
IPC: D05B69/16
Filed: 1961-09-22
Abstract: 934,739. Change-speed ratchet gear; cams; ratchet gearing. MEFINA S.A. Sept. 22, 1961 [Sept. 26, 1960], No. 33977/61. Classes 80 (2) and 80 (3). In a change-speed ratchet gear for driving a control cam in a sewing machine, wherein a stepped cam block 20, axially slidable on a driving shaft 4 reversely and intermittently rotates a driven shaft 46 through its steps 21, 22 or 23, a follower 18, a spring-loaded pawl 48, a ratchet-wheel 47 and a worm and wheel 43, 44, the block 20 comprises two cylindrical concentric portions 24, 26 which, when aligned with the follower 18, respectively move the pawl 48 into positions of one-way locking engagement with, and withdrawal from; the ratchet-wheel, and the longer of two diametrically opposite rods 40 extending axially from the block 20 clutches the block to the ratchetwheel for forward direct drive when the block is moved to align the concentric portion 26 withthe follower. To facilitate passage of the follower a supplementary eccentric portion 25 having an eccentricity equal to half the difference of the radii of the concentric portions 24, 26 is arranged therebetween so that its diametrically opposite generatrices are common with generatrices of the concentric portions, and the cam stops 21, 22, 23, the concentric portion 24, and the eccentric portion 25 have a common generatrix. The driving shaft 4 has secured thereto a driving belt pulley 5 and, by a radial pin 7, a collar 6. The rods 40 extend through the collar 6 to secure the block 20 circumferentially with respect to the shaft 4. The longer of the rods 40 is engageable, by its end 63, in a helical groove 61 and bore 62 in the adjacent face of the ratchet-wheel to clutch the latter to the block. A ring 9, on which the pawl 48 is pivoted at 13, surrounds the collar 6 and is frictionally gripped between a flange 8 of the collar and a spring washer 12 reacting on a ring 10 supported by the pin 7. To adjust the pressure of the spring washer, the ring 10 may be rotated to bring different depth notches thereon into engagement with the pin 7. The resultant frictional drag between the collar 6 and the ring 9 returns the pawl 48. The follower 18 is carried on a lever 16 which is pivoted on a base-plate 1 and to a link 14 also pivoted at 13 to the pawl 48 and ring 9. A back-stop, spring-loaded pawl 49 is pivoted on the base-plate and has a peg 51 engageable with a cam surface 52 on the ring 9 so as to be withdrawn from the ratchet-wheel simultaneously with the withdrawal of the pawl 48 which is effected by the engagement of its heel 53 with an adjustable stop 54. A slide 29 having a peg engaging a groove 28 in the block 20 is leftwardly moved, against a spring 38, to axially shift the block, by a notched cam 35 which moves over a scale 64. A further spring pawl 55 comprising a blade 56 secured to a member 57 pivoted on the base-plate is moved to engage the ratchet-wheel 47, by the action of an end 59 of the slide 29 on a part 60 of the member 57, only during clutching of the block 20 to the ratchet-wheel 47 for forward drive. In operation, as the cam 35 is moved through the scale positions " 18," 0, " 216 " to "108," the follower 18 successively engages the concentric portions 26, 24 and cam steps 23 to 21, respectively to withdraw the pawls 48, 49 and clutch the block 20 to the ratchet-wheel 47 for forward direct drive, to one-way lock the ratchet-wheel by the pawls 48, 49, and to reversely and intermittently drive the ratchetwheel 47 at speeds depending on which of the cam steps is engaged by the follower. Specification 918,043 is referred to.