GB436828A - Improvements in or relating to drive mechanisms - Google Patents

Abstract

436,828. Brakes. RADIO CORPORATION OF AMERICA, 30, Rockefeller Plaza, New York, U.S.A. Dec. 11, 1934, No. 35583. Convention date, Dec. 29, 1933. [Class 103 (i)] [See also Groups XXVI and XXXI] A drive mechanism for delivering a constant torque from a variable driving torque comprises a member driven by the variable-torque producing device, a device tending to subject it to a counter torque equal to the variable torque, and a device acting thereon for producing a constant difference between the driving and counter torques. In the device shown a spring 10 drives a shaft 14 with a brake wheel 24 secured to it. A brake shoe 19 carried by a pivoted toggle arm 20 carries a pawl 22 which engages in a ratchet 23 on the spring barrel 11. The reaction of the spring on the barrel acting through the pawl 22 thus tends to move the brake shoe 19 to the right, and by the action of the inclined toggle arm 20 to apply it to the wheel 24 so that the frictional counter-torque of the shoe is equal to the driving torque and rotation of the shaft 14 is prevented. The constant difference between the driving and counter torques is produced by a spring 18, of adjustable constant tension attached to the brake 19 and tending to move it to the left, in opposition to the pawl 22. In these circumstances, if r is the radius of the brake wheel, P the pull of the spring 18, and F the force exerted on the brake block by the pawl 22, then, since the brake block remains in equilibrium, the tangential frictional force produced by it on the wheel is equal to F-P, and results in a counter-torque of (F-P)r. Since the driving torque of the spring 10 on the drum is equal to Fxr, the resultant torque, that is, the difference between the driving and counter-torques, = Fxr-(F-P)r = Pxr. The effective driving torque is therefore equal to the product of the tension of the spring 18 and the radius of the brake drum, and is independent of the variations in torque produced by the spring 10. Other devices are illustrated in which the driven shaft is operated through gearing of epicyclic form from a hand-crank, the planetary or idler gears being mounted on a pivoted carriage connected to the brake so as to produce on it a force equal at all times to the driving torque, which force is opposed by a constant-tension spring as in the mechanism above described.