Pulleys 6 and 7 rotate about axes A and B of axles 8 and 9. These axles are connected by turning pairs to links 3 and 4 which can slide in fixed guides a and b. Screw 2 has right- and left-hand threads and is connected by screw pairs to links 3 and 4. When head 1 of screw 2 is turned, the distance between axes A and B is varied to obtain the required tension of flexible link 5 which runs over pulleys 6 and 7.
$3492$SFL,4L$