GB1110328A - One-way braking device - Google Patents

Abstract

1,110,328. Screw-and-nut gearing; safety devices. J. B. POPPER. 17 Aug., 1965 [20 Aug., 1964; 3 March, 1965], No. 35245/65. Headings F2J and F2Q. A one-way braking or locking device for driving a machine-tool lead-screw, jack, hoist, motor-vehicle window or steering-gear, or for opening and closing the door of a pressure chamber, or safety control of a press, uses differential screw-threads with proportions and friction coefficients related by specified formulae to give a desired degree of braking or locking with a high forward drive efficiency (exceeding 50%) without the necessity for a high reduction ratio. The device comprises a permanently fixed member 15; a first rotatable member 19 axially fixed with respect to the member 15; and a second rotatable and axially movable member 12 having differential screw-threads 13, 14 engaging threads on the members 15, 19. In Fig. 2, the member 12 drives and is turned by a handle 22, to impart rotation to the member 19 which is the driven member and has pinion teeth 21 engaging a rack carrying a vehicle window. In Figs. 1 and 5, not shown, the first rotatable member (10) and fixed member (6) have coaxial external threads engaging threads inside a sleeve (1) forming the second rotatable member. In Figs. 6 and 7 (not shown), the driven rotatable member is the ball-threaded lead-screw of a machine tool, which, in Fig. 7, not shown, is the second rotatable member, and so has axial as well as rotary movement. The differential threads may be of the same or opposite hand and the friction and thread parameters are related by the specified formulµ to give either simple one-way braking or three different degrees of self-locking as follows.- In a first order self-lock, locking occurs whenever the output attempts to drive the input. A second order self-lock adds to the first order, self-locking when the output member is subject to an active torque and the input member attempts to drive it in the same direction as that torque. (In this case the input drive would be unable to lower a load which it had raised). In a third order self-lock no drive is possible until a drive is applied simultaneously to both input and output. In this last form the device may be used as the safety control of a press, requiring both hands of the operator on input and output to control the press.